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University of Illinois Library
APR 12 1955
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UNIVERSITY OF ILLINOTS LIBRARY
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ysis JAN @ 2 1917
Reactions to Light in Vanessa Antiopa,
with Special Reference to
Circus Movements
“BY
WILLIAM LEE DOLLEY, Jr.
A Dissertation
SUBMITTED TO THE BOARD OF UNIVERSITY STUDIES OF THE JOHNS HOPKINS UNIVERSITY
IN CONFORMITY WITH THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
1914
BALTIMORE :
1916
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UNIVERSITY OF ILI INOIS LIBRARY
JAN 31 1917
Reprinted from Tue JOURNAL OF EXPERFMENTAL ZOOLOGY, Vol. 20, No. 3,
: April, 1916
REACTIONS TO LIGHT IN VANESSA ANTIOPA, WITH
SPECIAL REFERENCE TO CIRCUS MOVEMENTS
WILLIAM L. DOLLEY, Jr.
Professor of Biology, Randolph-Macon College
From the Zoélogical Laboratory of The Johns Hopkins University
TWENTY-ONE FIGURES
CONTENTS
ELEMIS Mey Pet eee a aH co s'E6 SE Fe aS ENS on CSN d io wiw Be ODT
RECEP E SEde nro RAIA 2 UR Act cia chy te < dale see sicvid aia dette R eam dald slccles 367
SE ES EE IOSEL OSB TES foe ae. weeseis Gin op less. 9 oss wine es Abn Wie. os wis bsp Bask tho 370
Behavior of specimens with but one functional eye....................... 371
A. Behavior in normal conditions of illumination........................ 371
me Genaviorin a beam ‘of-lighti.8 (0. co2.c.. cdi eee OF rd] PRE ae 371
1. Description of reactions—deflection, circus movements and orien-
SOONG Ss ig So RE Ae Oe ae eae ys a 371
2. Relation between the degree of curvature in circus movements and
Lee ULENELGY fac sadayhe Gt he Peek: c's (eae eRe e ee 382
3. Relation between the angle of deflection and the luminous inten-
SU loeione Jon lc Ggot ae erun ke Geee Cec ee nn ene en Coe 5 era 383
a. Effect of beginning the trials in different intensities........ 383
b. Effect of sudden changes of intensity on the angle of deflec-
SIU Pane OR eis a ae 4) cE Ae ths Pas PU bb de dated dies « 386
4. Reorientation after changing the direction of the beam of light.. 389
>. Effect of the covering of the eye owing to contact................... 394
SRIRESOHANION I NOR-CureCtL VG: MENG... shen eee Teens ces ccna eneeeeees ts 399
E. Relation between the degree of curvature in circus movements and the
luminous intensity of non-directive light.......................... 404
an titect OF INNMINAtING ONLY ONG CVO... 45.65 caus wend se veh aren Wyma 410
1. Effect of illuminating the entire surface of one eye.............. 410
2. Effect of illuminating different areas of one eye................. 413
See OIDINATY ANG CONCLUSIONIAS sac 5 in vata sid sata daWinn dandy dite tint tn =’ 415
NEON MLC el oer cc Sister, id Tete PHY ah oa Risley 06 W's, 5 MGR wha, Magda taialads des 419
INTRODUCTION
One of the most thorough pieces of work, which have been
done on the reactions to light itt butterflies, is that reported by
Parker (’03) on the mourning-cloak butterfly, Vanessa antiopa.
357
308 WILLIAM L. DOLLEY, JR.
This investigator found that these butterflies are highly positive
in their reactions to light, but that when they come to rest in
bright sunlight they ordinarily orient with the head directed
away from the source of light. He found, however, that when
one eye is painted black they do not orient, but continuously
creep or fly in curves with the functional eye toward the center.
Such reactions are usually called circus movements. This be-
havior, the author asserts (p. 463), is in accord with the view
‘“‘that the orientation of an organism in light is dependent upon
the equal stimulation of symmetrical points on its body.”
A number of other investigators have, also, recorded experi-
ments with other organisms in which circus movements have
been observed. Reactions of this nature have been reported in
experiments of three sorts: those in which one eye has been pre-
vented from functioning, either by being blackened, or by being
injured; those in which one antenna has been removed; and those
in which certain parts of the brain or of the inner ear have been
destroyed. .
In these experiments it has been found that photo-positive
animals, usually turn continuously toward the functional eye,
while photo-negative animals usually turn in the opposite direc-
tion. This is especially true in those cases in which one eye
has been covered. Holmes (’01 and ’05) and his students,
McGraw (13) and Brundin (’13), maintain that they have
observed this behavior in the following organisms: Hyalella den-
tata, Talorchestia longicornis, Orchestia agilis, two species of
bees, the robber fly, Asilus, Tabinus, a Syrphid, Ranatra, Noto-
necta, several beetles, Stenopelmatus, three species of flies, a
number of species of butterflies, and the amphipod, Orchestia
pugettensis. In all these cases, positive animals turned toward
the functional eye, while negative animals turned toward the
covered eye. ‘This, however, was not found to be true in all of
the species investigated. Holmes and McGraw (11, p. 370)
state that several species of butterflies, among them Vanessa
antiopa, frequently went in circles toward the covered eye, while
Brundin (13 p. 346) maintains that in positive specimens of the
amphipod, Orchestia traskiana, ‘“‘cireus movements will occur
REACTIONS TO LIGHT IN VANESSA ANTIOPA 359
as often toward the blackened eye as toward the normal eye.”’
Similar results have also been obtained with animals in which
one eye was injured. Réadl (01, p. 458) extirpated one eye of
the water scavenger beetle, Hydrophilus, and found that it de-
flected toward the side of the injured eye. Hadley (’08, pp.
180-199) seared with a hot needle the surface of one eye of larval
lobsters in all stages of development, and maintains (p. 198):
“The immediate results following this destruction of photo-
reception in one eye are: (1) The production of rapid rotations,
often at the rate of 150 per minute on the longitudinal axis of
the body, which are invariably in a determined direction. (2)
A type of progression in which the larva continually performs
‘circus movements’ or turns toward the side of the injured eye.”
Since these animals vary in the sign of their reaction to light at
different stages of development, it is interesting to note that
Hadley maintains that the circus movements made by animals
of all ages were all in the direction of the blinded eye. Mast
(10, p. 132) found that ‘‘Planaria with one eye removed, either
by gouging it out or by cutting off one side of the anterior end
obliquely, turn continuously from the wounded side for some
time, evidently owing to the stimulation of the wound, since,
after this is healed, they tend to turn in the opposite direction.”’
The destruction of the function of one eye is however not
always followed by circus movements. Rddl (’03, pp. 58-64)
states that Calliphora vomitoria is’ apparently not affected in
its behavior by having one eye covered, while Musca domestica,
although performing circus movements at times, can also ‘“‘run
‘rather long distances in one direction.’’ Carpenter (’08, pp.
483-491) blackened one eye of Drosophila ampelophila, and
reported that now and then one performed circus movements,
but he says (p. 486), ‘‘This conduct was exceptional, and was
never persisted in except in the case of a single insect which had
long been active and showed signs of fatigue.’’. They usually,
however, deflected somewhat toward the functional eye as they
proceeded toward the light. To quote further (p. 486), “‘They
crept in a fairly direct path toward the light, although a ten-
dency to deviate toward the side of the normal eye regularly
360 WILLIAM L. DOLLEY, JR.
occurred. The insects generally moved in a peculiar, jerky
manner. The tendency to diverge from the direct path toward -
the side of the uncovered eye was overcome by a series of short,
quick turns in the opposite direction, which kept them headed
toward the light.”” Mast (11, p. 222) found that the toad, Bufo
americanus, with the lens removed from one eye, hops or walks
toward a source of light, usually deflecting slightly toward the
injured eye. Some individuals, however orient nearly, if not
quite, as accurately after the operation as before. Thus, it is
evident that there are numerous exceptions to the idea that the
destruction of one eye is followed by circus movements.
Moreover, it has been found that some animals which make
circus movements modify their behavior after having had a cer-
tain amount of experience, and move directly toward the light.
Holmes (’05), in a detailed description of the behavior of one
specimen of Ranatra with the right eye blackened, says that in
the first ten trials before an electric light, it made many circus
movements, and showed a ‘‘marked tendency to turn to the
left.”’. In the next four trials it turned directly toward the
source of light and in the succeeding ten trials it reached the
light by a nearly straight path. After an interval of fifty min-
utes, eleven more trials were made, ‘‘and it had not forgotten
in the meantime how to reach the light by the most direct means,”
for it went to the light in every case in a nearly straight course.
The author also states that other specimens of Ranatra and
Notonecta showed this same modification. Brundin (713, pp.
334-352) observed similar reactions in the amphipods, Orchestia
traskiana and Orchestia pugettensis, except that being negative’
the animals turned toward the blackened eye. Mast tested on
two successive days a toad with one eye destroyed. He says
(11, p. 222): ‘The following day this toad was again exposed:
it now went toward the source of light even more nearly directly
than on the preceding day.”’ Thus, it is clear that the reactions
of at least some of these mutilated organisms may become modi-
fied as the result of repeated trials.
This is apparently not true of some animals. Rdadl cut out
one eye of Hydrophilus, and states that, though it lived for
REACTIONS TO LIGHT IN VANESSA ANTIOPA 361
several weeks in an aquarium, it never moved in a straight line,
but always in a course curved toward the side of the injured eye.
He says (’01, p. 458): ‘‘Es hat darnach noch mehrere Wochen in
meinem Aquarium gelebt, bewegte sich aber niemals gerade
sondern immer nur in einem Bogen concav nach der Seite des
extirpirten Auges.”’ This investigator (’03, p. 62) also observed
a fly, Dexia carinifrons, on the second day after its eye was
blackened and found its behavior was similar to that exhibited
immediately after the eye was covered, that is, it moved con-
tinually toward the functional eye.
The second group of experiments, as previously stated, refer
to insects with one antenna removed. V. L. Kellogg (’07, pp.
152-154) removed the left antenna from a male silk worm moth,
and found that when such an animal was placed three or four
inches from a female it ‘‘moved energetically around in repeated
circles to the right, or, rather, in a flat spiral, thus getting (usually)
gradually nearer and nearer to the female.’’ Males with the
right antenna removed turned continually to the left. In the
same year, Barrows (’07, pp. 515-537) removed the terminal
segment from one antenna of some fruit flies, Drosophila ampelo-
phila, and then, after twenty-four hours without food exposed
‘them to the odor of fermenting banana. He maintains that they
moved in circles toward the uninjured antenna in all but a few
cases in which they deflected in the opposite direction.
The third group of experiments mentioned comprises those in
which parts of the brain and inner ear have been injured or
removed. In these cases it is also maintained that the animals
make circus: movements.
It ean thus be seen that great diversity exists among the results
obtained by the various investigators in their experiments on
animals with the sense organs on one side destroyed. Among
these, those which refer to the eyes are of greatest immediate
interest to us. In these experiments it was found that while
photo-positive animals usually turn toward the functional eye
and photo-negative animals toward the non-functional eye, some
turn in the opposite direction and others orient fairly accurately,
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3
362 WILLIAM L. DOLLEY, JR.
while still others make circus movements for a period and then
orient fairly accurately.
This marked lack of harmony between the results obtained
may in some measure, at least, be due to the fact that the num-
ber of sources of light was not the same in all of the experiments:
Parker does not state the conditions under which the specimen
of Vanessa antiopa used by him made circus movements. Radl
presumably performed his experiments before a window, i.e.,
under conditions in which the animals received some light from
many different directions. The same probably held also for the
work of Holmes on amphipods and .several insects. In some
experiments, however, as in those performed with Ranatra and
Notonecta, he worked in a ‘darkened room,’ and used for a source
of light a sixteen candle-power incandescent lamp. Brundin and
Carpenter also used a similar source of light. It is significant
indeed that in every case where a single source of light on the
same horizontal plane with the organism was used, at least some
trials are described in which no circus movements were made,
the animals moving in a fairly straight course toward the light.
This was true of Ranatra, Notonecta, Drosophila, Bufo ameri-
canus, Orchestia traskiana, and Orchestia pugettensis. On the
contrary, in none of the experiments but one, where the light’
conditions were not sharply defined, have the investigators re-
corded any other behavior than movements in circles. This
single exception is that described by Radl, in which Calliphora
vomitoria and Musca domestica with one eye blackened ran for
some distance directly toward a window.
The experiments described in the present paper show that in
the case of Vanessa antiopa, at least, a knowledge of the number
of sources of stimulation is of great importance in a discussion
of circus movements; for the same animals, which, in a hori-
zontal beam, moved toward the source of light in a fairly straight
course, performed circus movements continuously when placed
before a window, or when the single source of light was placed
above the animal so that the light was non-directive.t The
1 The term ‘non-directive light,’ as used in this paper, denotes diffuse illu-
mination.
REACTIONS TO LIGHT IN VANESSA ANTIOPA 363
reactions under the former conditions seem to indicate that
both eyes are necessary for orientation; those under the latter,
that only one eye is necessary. Consequently, if the butterflies
had been studied only in front of a window, the conclusions
would necessarily have been erroneous.
Circus movements have been held by many to have a very
important bearing on the question as to the nature of the process
of orientation.
Holmes discusses this question rather fully. He takes the
position that the performance of circus movements indicates a
direct or indirect connection between the impulses set up by
light in the two retinas and the tension of the muscles of the
legs or appendages on the two sides of the body, and that this
is a ‘“‘sort of mechanical reflex process.’’ To him the pleasure-
pain theory explains those cases in which orientation occurs
in these asymmetrical animals. He says (11, p. 54): ‘In most
crustacea, as in most insects, orientation is effected through the
unequal action of the appendages on the two sides of the body.
In a form which is positively phototactic, ight entermg one eye
sets up impulses, which, passing through the brain and nerve
cord, cause, directly or indirectly, movements predominantly of
flexion of the legs of the same side and of extension of the append-
ages of the opposite side of the body. If this is a sort of mechani-
cal process, we should expect that, in a positively phototactic
form, if one eye were destroyed or blackened over, the animal
would move continuously toward the normal side.’”? Mindful
of the fact that the Ranatras and Notonectas in time straightened
their courses, and followed the light nearly as precisely as if they
had the use of both eyes, he also concludes that ‘‘ Phototaxis
may fall, to a certain extent, under the pleasure-pain type of
behavior. . . . . Light, in some animals, is followed much
as an object of interest is pursued by a higher’ animal” (’11,
p- 55). To these conclusions Brundin (’13) assents.
According to Carpenter, the local action theory of tropisms
would explain circus movements, were it not that some animals
with one eye blackened can orient, as accurately as if both eyes
were functional. The pleasure-pain theory, he holds, explains
364 WILLIAM L. DOLLEY, JR.
this behavior. He says (’08, p. 486): ‘‘It is clear that the tropism
theory, with its assumption of local action of stimulus on the
side exposed to its effect, does not furnish a complete explanation
of these reactions. . . . . A ‘pleasure-pain’ reaction appears
to inhibit and dominate a ‘tropic’ reaction.”
To Radl, cireus movements are an evidence of inequality in
the tension of the muscles on opposite sides of the body, pro-
duced by the blackening of one eye. He says (’038, p. 63): ‘Bei
einem Tier, dem ein Auge geschwiarzt wurde, erschlaffen etwas
die Muskeln an der Ko6rperseite, wo das Auge nicht sieht; da sich
nun die Muskeln der anderen Seite kraftiger bewegen, so erfolgt
eine Bewegung in einer nach der Seite dieser stirker arbeitenden
Muskeln gekriimmten Bahn.”
Parker (’03, p. 463), as has been previously stated, maintains
that the circus movements he observed in Vanessa antiopa are
in accordance with the view ‘‘that the orientation of an organism
in light is dependent upon the equal stimulation of symmetrical
points on its body.” He says further: ‘‘Should the eyes be the
parts stimulated, any interference with one of these ought to
result in a disturbance of the direction of the butterfly’s loco-
motion. Thus, if the cornea of one eye were blackened, the
insect in locomotion, being positively phototropic, ought to move
as though that eye were in shade, namely in a circle, with the
unaffected eye toward the center.”
To Barrows, who worked on the reactions of Drosophila to
odors, circus movements can only be explained by the ‘tropism
theory.’ He says (’07, p. 535): “It seems impossible to explain
the movements under these conditions in any other way than on
the basis of the tropism theory. This theory has been stated
in several ways. As applied to chemical stimulation, Verworn
(99, p. 429) declares: ‘The word chemotaxis is applied to that
property of organisms that are endowed with the capacity of
active movement by which, when under the influence of chemi-
cal stimuli acting unilaterally, they move toward or away from
the source of the stimulus.’ ”
V. L. Kellogg (07) and Bohn (11) agree with Loeb, whose
views are given in the next paragraph, and Bohn even cites
circus movements as one of his criteria for tropisms.
REACTIONS TO LIGHT IN’ VANESSA ANTIOPA 365
Loeb (706, p. 140) attempts to refute any notion of a pleasure-
pain type of behavior in lower organisms, and accepts the phe-
nomenon of circus movements as a fact in support of his theory
in explanation of the orientation of animals. This is discussed
fully in the Mechanistic Conception of Life. (12, p. 35-62.)
He holds that the orientation of animals is controlled unequivo-
cally by external agents, and that in orientation to light, there
are two essential factors, the continuous action of light and the
symmetrical structure of the organisms. According to his view,
which may be called the ‘continuous action theory,’ the tension
of the muscles of the appendages on the two sides of the body is
controlled through direct reflex arcs by the photochemical changes
produced by light in the two retinas. He says (’12, p. 39):
“When two retinae (or other points of symmetry) are iJluminated
with unequal intensity, chemical processes, also of unequal in-
tensity, take place in the two optic nerves (or in the sensory nerves
of the two illuminated points). This inequality of chemical
processes passes from the sensory to the motor nerves and even-
tually to the muscles connected with them. We conclude from
this that with equal illumination of both retinae the symmetrical
groups of muscles on both halves of the body will receive equal
chemical stimuli and thus reach equal states of contraction, while
when the rate of reaction is unequal, the symmetrical muscles
on one side of the body come into stronger action than those on
the other side. The result of such an inequality of the action
of symmetrical muscles of the two sides of the body is a change
in the direction of movement on the part of the animal.”
It is clear that in this theory it is assumed that light is effective
in orientation through its continuous action, that after orienta-
tion has occurred, light continues to stimulate the photosensitive
areas, and through direct reflex arcs, continues to affect the
muscles of the appendages on the two sides of the body. These
assumptions, as stated above, are, according to Loeb, supported
by the behavior of animals with the sense organs functional only
on one side. He quotes Parker as follows (’06, p. 140): ‘‘ Loeb
has pointed out that the orientation of an organism in light is
dependent upon the equal stimulation of symmetrical points on
366 WILLIAM L. DOLLEY, JR.
its body. Should the eyes be the parts stimulated, any inter-
ference with one of these ought to result in a disturbance of the
direction of the butterfly’s locomotion. Thus, if the cornea of
one eye were blackened, the insect in locomotion, being positively
phototropic, ought to move as though that eye were in shade;
namely, in a circle, with the unaffected eye toward the center.”
Mast holds that the precision with which some organisms with
but one functional eye perform circus movements appears to
add support to the ‘continuous action theory,’ but he also says
(11, p. 222), as a result of his work on the toad, ‘‘ These results
show that, in this form and in all other forms which orient after
one eye is destroyed, difference of effective intensity on opposite
sides does not regulate orientation.”
A glance at these various views shows that the movement of
‘animals in circles when one eye is blackened, or when one antenna
is removed, has been held by most of the investigators to support
the view that the orientation of animals is in accord with the
‘continuous action theory’ described above. This theory is op-.
posed by one that may be called the ‘change of intensity theory,’
the adherents of which hold that in some organisms, at least, light
does not produce orientation through its continuous action, but
by stimuli dependent upon the time rate of change of intensity.
According to this theory, an organism going toward a source
of light, may turn to one side; but when this occurs, then, imme-
diately the photosensitive surfaces are exposed to a change of
intensity, and this causes a reaction which results in reorienta-
tion, after which the orienting stimulus ceases.
The chief points at issue between the two theories concern the
following questions: (1) Does light function in orientation through
its continuous action, or through a change of intensity? (2)
Does an animal, when oriented, continue to be affected by the
same stimulus that is effective in producing orientation? and
(3) Is bilateral symmetry essential in the process?
In view of the bearing that circus movements have on the
theories as to the mechanism of normal orientation in animals,
and in view of the conflicting results recorded by previous workers
it seemed desirable to make a more thorough and a more extended
REACTIONS TO LIGHT IN VANESSA ANTIOPA 367
study of this phenomenon than has been done previously. More-
over, such a study should throw light on the question as to
whether or not the path of nerve impulses resulting in a given
reaction can be altered, as well as on the very important prob-
lem of modifiability in behavior in general.
The mourning cloak butterfly, Vanessa antiopa, was chosen
to begin with because the results secured with this animal by
Parker are widely known and frequently quoted. This work is
to be followed by a more general study of the phenomenon in
question.
Before entering upon a discussion of these experiments I wish
to express my very sincere appreciation of the kindness of Pro-
fessor S. O. Mast in suggesting this problem to me and in so
unselfishly aiding me throughout the course of the work.
METHODS
The butterflies used were all reared in the laboratory from
larvae secured from both the June and the August broods in
Massachusetts, New York, and Pennsylvania. No difficulty was
experienced in keeping them in excellent condition for long periods.
They were kept in the laboratory in a large glass case, and fed
on honey and a weak solution of maple syrup in water. At
frequent intervals the insects were picked up and dropped on
filter paper soaked in the latter sweet mixture. If the proboscis
was not extended at once, it was uncoiled with a pin, and when
once the tip touched the liquid, the animal continued to feed
until its abdomen was swollen to an extent which seemed dan-
gerous. Since these butterflies pass the winter in the imago
state, it is not surprising that six specimens lived from August
until the latter part of February. These were the survivors of
a lot of about thirty which were received at the same time.
Had proper care been taken, it is likely that nearly all would
have. lived through the winter in the laboratory. The wings of
the butterflies were-usually clipped to prevent their escape. This
was in no wise injurious, for animals with clipped wings lived
and thrived at well as those whose wings were intact, and they
behaved in the same manner.
368 WILLIAM L. DOLLEY, JR.
As already stated, three methods have heretofore been used
to preyent the functioning of one eye; extirpation, searing with
a hot needle, and covering with asphalt varnish. The latter
method was used exclusively in the present work, because it was
believed that fewer disturbing factors would be introduced
thereby.
In the early part of the work, one eye was covered with one
or two coats of the asphalt varnish. After having made some
experiments with animals treated thus, it was found, to my sur-
prise, that insects with both eyes covered in this way still oriented
fairly precisely, and went toward the source of light. Thus it
is evident that the varnish as used did not exclude all of the
light. The eyes were then painted repeatedly until the coats
were so thick as to be distinctly evident when the observer was
several feet from the butterflies. Under these conditions the
animals were indifferent to light. Warned by this experience,
the blinded insects used in all future experiments were so treated
that it seemed certain that the eye was in every case effectively
covered. Moreover frequent examinations were made to make
sure that the varnish had not cracked or fallen off; and new
coats were from time to time applied to make assurance doubly
sure.
In work of this sort it is important that the varnish be of such
nature that it does not injure the eye in any way. The effect
of the covering was consequently repeatedly tested by removing
it from the eyes after it had been on for some time. Insects
thus tested behaved as did those whose eyes had not been
blackened, showing no effect from the varnish.
The supply stock of butterflies was ordinarily kept in a large
cage which was four feet high, four feet long and two feet wide.
This was fastened against a south window in such a way that
the window formed one side of the enclosure. The opposite side
was also of glass and faced a small laboratory room. The other
two sides, the top, and the bottom, were of wood. Careful
observations were made on the insects in this enclosure, from
time to time, throughout the whole period over which the experi-
ments extended. But a much more thorough investigation of
REACTIONS TO LIGHT IN VANESSA ANTIOPA 369
the behavior in light was made in a dark room under accurately
controlled environmental conditions. In these experiments the
animals ‘were exposed in a horizontal beam produced by means
of a 110 volt Nernst glower. The glower was mounted in front
of a small opening in a light-proof box that was painted dead
black inside, so as to form a non-reflecting background. It was
placed 10 cm. from and at the same level with the top of a table
on which the animals were tested. By means of screens the
light from the glower was so cut down as to produce a sharply
defined beam of the size desired. The edges of this beam could
be clearly seen on the black top of the table. This beam was
the only light in the room, and this was in large part absorbed
by means of dull black paper hung over the exposed walls.
There was consequently very little ight in the room aside from
that in the beam. Under these conditions therefore, the animals
were exposed in a beam of light from a single, small and con-
centrated source.
The limits of this beam were very apparent in the dark room
in which the experiments were made. ‘The nature of the source
of light and the sharply defined character of the beam are im-
portant, for experiments described later demonstrate that the
behavior of animals with one eye blackened depends to a marked
* extent upon whether there are one or more’ sources of light
present.
Not only was the behavior of the animals described by the
observer, but the butterflies, themselves, were forced to make
permanent records of their own behavior. This was done by
allowing them to walk on sheets of paper which had been covered
with soot from an oil lamp. These sheets measured 20 x 25 cm.,
but in some experiments, a number of them were placed side by
side until the area was as large as desired. The tracings made
by the insects were made permanent by means of a coat of
shellac. The butterflies were frequently allowed to walk over
the sheets of paper covered with soot, and then the same experi-
ment was repeated without ‘the use of the blackened paper.
The same results were secured in both cases. This shows that
the behavior was not affected by the soot. This method of hav-
370 WILLIAM L. DOLLEY, JR.
ing the animals make permanent records of their own behavior
is most valuable, for the records can be kept indefinitely and
studied, thus giving opportunity to recognize many significant
features which otherwise might have been overlooked at the time
the experiments were performed. It would be of value, no doubt,
to the keenest observer.
BEHAVIOR OF NORMAL SPECIMENS
In the study of normal animals in the cage referred to above,
Parker’s observations were confirmed. It was found that the
insects were highly positive in their reactions to light. During
the day, in the absence of direct sunlight, they were usually in
active movement, flying against the window. Occasionally an
animal would fly around the cage, but this was exceptional.
When at rest the butterflies were usually grouped on the window
side of the cage, where they assumed various positions on the
bottom of the window sash, some facing the light, others in a
horizontal position at right angles with the rays, some hanging °
on the sash in a vertical position with their heads up, and others
hanging with their heads down.
When the sun was so situated that the butterflies were exposed
directly to its rays, and they were undisturbed, they usually
ceased their active movements and oriented very definitely. ~
They turned so as to face directly away from the sun and spread
their wings to their fullest extent, exhibiting behavior similar
to that described by Parker. This position was retained indefi-
nitely unless the insects were disturbed.
In a beam of light in the dark room the responses were quite
different. In making observations under these conditions the
animals were placed in the beam at various distances from the
glower so that they faced the-source of light. As soon as they
were released they usually darted directly toward the glower and
continued until they reached the edge of the table. The insects
were always found to be highly positive in all intensities in which
they were tested. They never exhibited the slightest indication
of negative reactions. ‘They never came to rest with the head
directed from the light and the wings spread, as they usually
did in direct sunlight.
REACTIONS TO LIGHT IN VANESSA ANTIOPA 371
BEHAVIOR OF SPECIMENS WITH BUT ONE FUNCTIONAL EYE
A. BEHAVIOR IN NORMAL CONDITIONS OF ILLUMINATION
In normal conditions of illumination the behavior of butter-
flies with but one functional eye was very different from that
described above. Such specimens were tested on the floor of
the cage referred to previously, on a table before a window, and
in a beam of light in the dark room. Before a window and on
the floor of the cage it was found that whenever they moved
they turned continuously toward the functional eye, exhibiting
_ behavior similar to that described by Parker. The periods of
activity, which in some cases lasted for several minutes, alter-
nated with periods of rest in which the animals remained practi-
cally motionless, as if recovering from fatigue. But the point
that is of especial interest is that they continued to make circus
movements from day to day, and that they did not learn to orient.
Two insects with one eye blackened were kept for twenty-three
days, and although they were observed many times each day no
modification in their behavior was detected. In this respect,
however, the reactions in a beam of light differed greatly.
B. BEHAVIOR IN A BEAM OF LIGHT
1. Description of reactions—deflection, circus movements, and
orrentation
Under the conditions of illumination described in the preced-
ing paragraph, the animal receives light from all sides, and all
the large areas of the functional eye are approximately equally
illuminated in every position assumed by the insect. When
exposed to the light in a beam the animal receives light from
only one direction, and consequently every movement that is
not directed toward the glower produces a change in the illumi-
nation of different large areas of the uncovered eye. This may
account for the difference in behavior observed under the two
conditions of illumination.
The behavior in a beam of light of Vanessa with one eye
blackened was studied in 46 different individuals and many of
ake WILLIAM L. DOLLEY, JR.
these were tested on several successive days. In nearly all cases
the animals were forced to record their reactions on carbon
paper, as previously described. In all tests the butterflies were
placed in the beam so that they faced the light directly. The
results obtained varied considerably in different individuals and
also in the same individual under different conditions. In some
respects, however, there was but little variation.
Nearly all of the butterflies tested turned toward the functional
eye immediately after they were exposed, regardless of the
luminous intensity or the axial position with reference to the
Fig. 1 Reproduction of various trails made by different specimens of Vanessa
with the left eye blackened when exposed in a beam froma Nernst glower. The
diverging straight lines represent the limits of the horizontal beam. The arrows
indicate the direction of motion. Their trails show that there is great variation
in the reactions of different individuals under the same conditions.
direction of the rays of light. Some of them continued to turn
in this direction making repeated circus movements? (fig. 1, a
and b) until they became fatigued and stopped, or until they
reached the edge of the beam, where many turned sharply toward
the glower and traveled along the edge of the beam toward
the source of light, as is shown in figure 1, c. A few, however,
did not turn toward the light when they reached the edge of the
beam, but passed into the shaded region, continuing to make
circus movements (fig. 1, e€). Others did not make circus move-
ments, but turned until the longitudinal axis made a certain
2 In the present paper the term ‘circus movements’ with no further explanation
means continuous movement toward the functional eye.
REACTIONS TO LIGHT IN VANESSA ANTIOPA 373
angle with the rays of light, and then continued until they
reached the edge of the beam. Here they usually turned sharply
toward the glower and moved along the edge of the beam toward
the source of light (fig. 1, f) but occasionally they continued to
turn here and made circus movements (fig. 1, 7), and sometimes
they did not respond at all when they reached the edge of the
beam, but continued until they had passed into the shaded region
from 2 to 5 em. when they usually turned and proceeded directly
toward the glower, remaining in this region (fig. 1, g). Ona few
occasions, however, they did not turn when they reached the
edge of the beam, but proceeded on in the shaded region indefi-
nitely (fig. 1, h). A few animals did not turn toward the func-
tional eye, but oriented fairly accurately and walked toward the
glower in a nearly straight course (fig. 1, k). Several specimens
in some trials turned toward the blackened eye, crossed the beam,
and on reaching the edge turned and walked along it toward the
source of light (fig. 1, 7).
Many insects, as the trials proceeded, showed an increase in
accuracy of orientation. This was evident in three respects: (1)
in the number of circus movements made, (2) in the angle of
deflection, and (3) in the promptness with which they oriented
at the edge of the beam.
The above general description may perhaps be made clearer
if the reactions of one organism are described in detail. This
animal designated as butterfly 10/25-a (left eye blackened) was
tested on three successive days.
On the first day this butterfly was given twenty trials (fig. 2).
In every one it turned toward the unblackened eye immediately
upon being placed in the beam. In the first trial it crossed the
beam at an angle of approximately 95 degrees with the rays of
light, and passed into the shaded region. After it had gone 6
em. in this region it turned to the left (the blinded eye) and
walked toward the glower in a slightly zig-zag course, remaining,
however, in the comparative darkness to the right of the beam.
In the second trial, after crossing the beam at an angle of nearly
80 degrees, it again went to a point 6 cm. beyond the edge of the
beam, but then it turned sharply to the right (toward the func-
374 ; WILLIAM L. DOLLEY, JR.
tional eye) and performed a circus movement. ‘This was fol-
lowed by a fairly straight course for 7.5 em. At this point the
organism turned again to the right as if to make a circus move-
ment but did not complete it, turning instead to the left toward
the source of light. In the third trial the insect made a circus
movement as soon as it was placed in the beam and then crossed
the beam at an angle of about 95 degrees with the rays of light,
and went 3 em. into the shaded region where it turned toward
the blackened eye and moved in a course nearly parallel with
the edge of the beam. In the fourth the behavior was like that
in the preceding trial except that after the organism passed the
Fig. 2 Reproduction of 20 successive trails made by butterfly 10/25-a (left
eye blackened) on the first day of the tests. aand b, limits of horizontal beam of
light; 1-20, trailsmade in successive trials; small arrows, direction of movement
of animal; large arrows, direction of rays of light; illumination at x, 624 mc.;3
at y, 250 mc.
edge of the beam it did not turn toward the glower, but con-
tinued on in a fairly direct course until it reached the edge of the
table. In the fifth trial the butterfly continued across the beam
at about the same angle as in the previous trials until it had
gone 2.5 cm. beyond the edge. At this point it turned toward
the blackened eye and moved fairly directly toward the glower.
In the sixth the organism again made a circus movement imme-
diately upon being placed in the beam. It then crossed the
beam at right angles with the rays, and on reaching the right
3 Throughout this paper the abbreviation ‘me.’ will be used to indicate meter-
candles. ,
REACTIONS TO LIGHT IN VANESSA ANTIOPA 315
edge, immediately turned toward the blackened eye and moved
along the edge of the beam toward the glower. In the seventh,
eighth, and in the twelfth to the nineteenth trials the behavior
of the butterfly was essentially the-same as in the fifth, but it
usually went further in the shaded region before turning toward
the glower, this distance varying from 2.5 to 14cm. After orien-
tation, however, it continued to move in all cases fairly directly
toward the glower. In the tenth and third trials, the behavior
was essentially similar. In the ninth, eleventh, and twentieth
the reactions were also very much alike, the organism in each
trial curving gradually toward the functional eye, in this way
passing beyond the edge of the beam into the shaded region
outside, and then coming back to the edge. again. On reaching
the edge of the beam the second time the butterfly turned much
more sharply toward the functional eye, thus completing a circus
movement and at the same time arriving at the edge of the beam
a third time. When this occurred, the insect turned toward the
glower and moved along the edge of the beam toward the source
of light. :
These reactions in the trials on the first day of the tests show:
(1) that Vanessa with but one functional eye tends to turn toward
this eye when placed in a beam of light; (2) that it can orient;
(3) that orientation does not usually occur in the beam, but
does occur either at the edge of the beam or several centimeters
beyond it; (4) that after circus movements have been performed
in a given trial the animal often orients and moves directly toward
the source of light; and (5) that a change in illumination seems
to favor the performance of circus movements, since, out of 8
circus movements, 4 were made almost immediately after the
insect was placed in the beam and before it had reached the
edge of the beam, 3 were made at the edge of the beam, and only
1 was made elsewhere.
On the second day in all of the first eight trials, except the
fifth, the butterfly assumed an angle of about 90 degrees with
the rays, and then traveled across the beam and into the shaded
region for a distance of from 1.5 to 9 cm. where orientation
occurred (fig. 3). In the fifth it continued on to the right in
376 WILLIAM L. DOLLEY, JR.
a moderately straight course until it fell off the table. The
behavior in the next three trials was very much alike, the organ-
ism performing a circus movement upon first being placed in the
beam, and then, after having gone a few centimeters beyond the
edge, it turned and went toward the glower. The eleventh trial
is interesting in that, although the organism was started very
much nearer to the glower, and consequently in much stronger
Fig. 3 Reproduction of 34 successive trails made by butterfly 10/25-a (left
eye blackened) on the second day of thetests. a and b, limits of horizontal beam of
light; 1-34, trails made in successive trials; small arrows, direction of movement
of animal; large arrows, direction of rays of light; illumination at x, 624 me.;
at y, 250 me.
light, it, after having performed a circus movement, deflected
at an angle of only 40 degrees with the rays of light, while in
several of the previous trials in which it had started further
away from the source of light it deflected at a much greater
angle. In the twelfth trial the butterfly made a circus move-
ment when first started and then after having gone 1.5 em.
beyond the edge of the beam it again performed a circus move-
ws
REACTIONS TO LIGHT IN VANESSA ANTIOPA old
ment. This was followed by a zig-zag course nearly parallel
with the edge of the beam. This circus movement is worthy
of notice for it was made.in the shaded region outside the beam,
when the animal was in very weak light. It should also be
noted that the diameter of the curve made is very nearly the same
as the diameter of the curve made in the beam in comparatively
strong light, when the insect was first started in this trial. This
peculiarity will be correlated later with the results of other experi-
ments. In the thirteenth trial after performing a circus move-
ment in the beam the organism continued to the right in a fairly
straight course to the edge of the table. In the fourteenth a
circus movement in the beam was made, and then the animal
went 7 cm. beyond the edge and oriented, moving toward the
glower. In the fifteenth it crossed the rays of light and made
a circus movement to the right of the beam. It then went toward
the glower in a fairly straight line, but before reaching the source
of light it made another circus movement. In the sixteenth a
circus movement was made to the right of the beam. This was
followed by a zig-zag course toward the glower. The behavior
in the succeeding eighteen trials was essentially similar to that
described above. It should be noted, however, that in the
twenty-fourth trial the butterfly after moving to the right until
the edge of the beam was reached turned more sharply toward
the functional eye at this point. It did not, however, perform
a circus movement, but gradually turned to the left. This sharp
turn toward the functional eye on reaching the edge of the beam
seems to support the conclusion arrived at from the trials on the
previous day, namely, that change in illumination tends to favor
the performance of circus movements.
These trials on the second day thus confirm strongly the con-
clusions drawn from the reactions on the first day, and they show
moreover that after a certain amount of experience the angle of
deflection tends to decrease, for on the first day the average
angle between the path of the butterflies and the rays of light
was 100 degrees while on the second day it was only 89.5 degrees.
The reactions on the third day (fig. 4) differed very markedly
from those described for the first two days in several respects.
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3
‘
378 WILLIAM L. DOLLEY, JR.
In all but the fourth and fifth trials the organism turned toward °
the functional eye, crossed the beam at a definite angle which
was smaller than on the preceding days, and, on. reaching the —
edge of the beam, turned at once to the left and walked along
this edge toward the glower. In the fourth trial it responded
very much like a normal specimen, walking down the center of
the beam in a fairly straight line. In the fifth it deflected toward
the blackened eye. No circus movements were made in any of
the trials on this day.
Fig. 4 Reproduction of 23 successive trails made by butterfly 10/25-a (left ~
eye blackened) on the third day of the tests. a and b, limits of horizontal beam
of light; 1-23, trails made in successive trials; small arrows, direction of movement
of animal; large arrows, direction of rays of light; illumination at x, 906 me.; at
y, 266 mc. Compare figures 2, 3 and 4 and note that the insect on the third day
made no circus movements, while on the two preceding days, it made numerous
ones. Note also that the angle at which it deflected with the rays of light
decreased.
By comparing all of the reactions observed during the three
days it will be seen that modification occurred in three different
respects, as follows: (1) On the first two days there were numer-
ous circus movements; on the third day there were none what-
ever; (2) On the first two days the butterfly usually passed into
the shaded region a considerable distance before it turned and
went toward the glower; on the third day it turned toward the
glower promptly on reaching the edge of the beam; (8) The
angle of deflection was greatest on the first day and least on the
third, the average angle at the edge of the beam for the three
days being respectively 100, 89.5, and 41.5 degrees. The reac-
REACTIONS TO LIGHT IN VANESSA ANTIOPA 379
tions of three other insects showing similar behavior are pre-
sented in figures 5, 6 and 7.
The results presented in these figures as well as in the preced-
ing ones seem to show that butterflies with but one functional
eye improve in the accuracy of orientation with experience. This
conclusion and others are strongly supported by the results
yh tl
t
t yO obi lalz
Fig.5 Reproduction of 15 successive trails made by butterfly 7/29-c (right eye
blackened). a and 6, limits of horizontal beam of light; 1-15, paths made in
successive trials; small arrows, direction of movement of animal; large arrows,
direction of rays of light; illumination at z, 4892 mc.; at y, 544 mc. Note that
this insect made three circus movements in the first four trials, while in the next
eleven trials it made none.
obtained in all of the tests made. These are briefly summarized
in table 1.
This table will be clearer if a brief explanation of some of the
data is given. In the columns headed ‘Direction turned’ is
stated the direction toward which the butterflies turned 7mmedi-
ately after they were placed in the beam. The average angle
of deflection was ascertained in the following way. The angle
380 WILLIAM L. DOLLEY, JR.
between the rays of light and the trail of the insect at the edge
of the beam in each of the trials was measured. ‘This angle is
termed the ‘angle of deflection.’ The average then was com-
puted for a number of the first trials on each day, this number —
being equal to the number of trials on that day on which fewest
trials were given. The columns marked ‘Place where orientation
Fig.6 Reproduction of 40 trails made by butterfly 10/1-b (left eye blackened).
A, 1-20, trails made in successive trials on the first day of the tests; B, 1-20, trails
made on the second day of the tests; a and b, limits of horizontal beam of light;
small arrows, direction of movement of animal; large arrows, direction of rays
of light; illumination at x, 925 mc.; at y, 266 mc. Note that this insect modified
its reactions in that it made numerous circus movements in the trials on the
first day, but made none in the trials on the second day.
occurred’ also demand some explanation. By ‘Orientation’ is
meant the assumption of an axial position with the head pointed
directly toward the glower followed by movement in this direc-
tion. If the animal turned and moved directly toward the source
of light before it reached the edge of the beam it is said to have
oriented ‘in the beam.’ If it, however, went more than one centi-
meter beyond the edge before it turned toward the glower it is
.
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TABLE 1
Summary of reactions in a beam of light of 46 specimens of Vanessa antiopa with but one functional eye
DISTANCD NUMBER OF PLACD WHERE
rH GLOWER OREN ORG gornicans ORIENTATION OCCURRED
DESIGNATION IN TOTAL AveRkGm | — pees oh
a aa brittle Svs see Ie, oe N
Som ete a PER DAY besa Toward] nig not] In |Outside| PEFEECTION | In aes te als a Ne
TRIALS WERE tional |°°Vee4] “turn | beam | beam beam | of | a iiton ae
BHGUN eye eye beam
October
13 23-45 21 Left 21 0 0 31 1 99.0 0 9 10 2
10/13-a..... u 23-45 22 Left 22 0 0 1 0 65.0 0 19 2 1
15 23-45 21 Left 21 0 0 1 1 60.0 0 18 2 1
16 23-45 21 Left 19 0 2 0 0 35.0 0 19 0 2
October
13 23-45 22 Right 22 0 0 72 5 97.0 0 16 5 1
10/18-b..... 4 23-45 7 Right 7 0 0 1 0 100.0 0 4 3 0
15 23-45 20 Right 20 0 0 28 2 81.4 0 il 4 5
7 23-45 20 Right 20 0 0 1 0 69.2 1 4 13 2
October
10/l4-a..... 14 25-60 21 Left 21 0 0 8 0 78.2 0 19 1 1
15 18-45 21 Left 21 0 0 0 0 54,2 0 20 1 0
17 20-45 20 Left 20 0 0 0 0 43,2 0 20 0 0
October
10/25-a..... 25 28-45 20 Right 20 0 0 4 4 100.0 0 4 15 1
26 28-45 34 Right 34 0 0 4 4 89.5 0 4 24 6
27 15-43 23 Right 22 0 1 0 0 41.5 1 18 3 1
October
Tbjacse 6 23-45 20 Left 20 0 0 18 0 101.2 ) 10 5 5
ae 7 25-80 20 Left 15 5 0 0 0 30.0 4 re) 4 0
8 28-80 20 Left 10 9 1 0 0 14.7 0 14 0 6
October
10/1-a...... } 1 28-45 41 Left 41 0 0 25 30 78.0 2 0 1 38
2 28-45 30 Left 28 1 1 0 5 50.0 1 ll 0 18
October
2 23-45 20 Left 20 0 0 2 0 81.8 0 4 11 5
pa ‘ 25-45 20 Left 19 0 1 0 0 37.5 3 12 4 1
4 23-45 21 Left 21 0 0 0 0 54.3 2 18 1 0
5 18-45 20 Left 0 20 0 0 0 46,2 0 19 0 1
6 20-47 21 Left 16 5 0 0 0 42.5 0 21 0 0
July
24 30 21 Left 18 2 1 0 2 62.0 3 8 4 6
7/24-4-a... 25 30 35 Left 29 4 2 0 0 49.0 3 14 4 14
26 30 10 Left 7 2 1 0 0 31.5 i 6 0 3
27 30 10 Left 7 0 3 0 0 23.5 3 7 0 0
July
7/11-3 ll 30 21 Left 19 2 0 0 1 44.2 0 it 0 20
he 12 “30 51 Left 45 6 0 0 0 35.0 2 4 6 39
13 30 40 Left 15 8 17 0 0 11.0 19 itt 2 8
October
10/8-c..... 7 8 18-78 22 Left 22 0 0 0 2 44,3 0 15 5
9 28-82 23 Left 19 at 3 0 0 14.5 3 19 0 1
October
10/24-a..... 4 24 25-82 20 Left 19 0 1 17 0 110.7 0 16 0 4
25 25-65 21 Left 21 0 0 98 3 88.5 0 9 5 7
October
10/14-b } 14 18-45 33 Right 31 2 0 22 3 86.3 0 19 10 4
‘eee 15 18-45 20 Right 19 0 if 17 2 83.0 2 14 0 4
L 16 18-45 21 Right 21 0 0 2 i 0 ll 10 0
September
9/21-8 21 18-28 5 Right 5 0 0 1 0 107.0 0 2 3 0
3° ae 22 28-45 10 Right 10 0 0 0 0 53.0 0 10 0 0
23 23 Right 23 0 0 0 0 0 23 0 0
October
10/8-a...... 4 8 40 Left 38 1 1 0 1 71.5 8 28 3 1
9 20 Left 18 2 0 0 0 29.75 0 19 0 1
July
7/16-0..... 16 30 17 Left 17 0 0 0 3 62.3 2 14 1 0
July
7/29-c....+. 29 30 15 Left 7 0 8 0 3 20.6 8 6 1 0
September
22 30 25 Right 25 0 0 0 0 67.5 0 3 16 6
23 30 21 Right 20 1 0 0 0 62.5 0 il 9 1
24 45 20 Right 9 9 2 1 0 25.5 2 15 1 2
9/22-c..... 4 25 23-45 20 Right 20 0 0 0 0 62.0 0 20 0 0
26 23-45 21 Right 21 0 0 f 3 79.0 0 13 0 8
27 25-45 26 Right 26 0 0 0 0 51.5 0 26 0 0
29 23-45 32 Right 32 0 0 0 0 51.0 0 32 0 0
30 17-45 32 Right 32 0 0 0 0 57.2 1 29 2 0
September
22 28 45 Left 45 0 0 1 2 85.7 0 1 18 26
24 45 20 Left 20 0 0 1 5 39.2 0 12 1 vf
9/22-b 25 45 21 Left 14 2 5 0 0 34.7 5 10 4 2
aie a 26 23-45 33 Left 31 0 2 1 0 60.7 2 9 15 - 7
27 20-45 36 Left 32 0 4 0 0 40.5 4 32 0 0
29 23-45 20 Left 20 0 0 2 0 A 0 13 4 3
30 18-45 30 Left 28 1 1 0 0 56.0 1 19 9 1
October
1 23-43, 20 Right 20 0 0 9 2 67.7 0 9 9 2
2 23-45 20 Right 19 st 0 0 0 41.5 0 16 4 0
10/1-b 3 23-43 20 Right 20 0 0 0 0 55.2 0 12 7 1
ra Bk 4 23-45 20 Right 20 0 0 0 0 68.7 0 18 2 0
5 23-45 21 Right 21 0 0 0 0 63.2 0 19 2 0
6 23-80 24 Right 24 0 0 0 0 36.0 0 24 0 0
7 20-80 27 Right 26 1 0 0 0 33,7 0 26 0 a
July
7/8-3 8 30 73 Left 58 10 5 3 10 36.5 11 17 16 29
A Sareea A) 9 30 58 Left 51 4 3 3 14 51.0 4 9 8 37
10 30 33 Left 18 8 7 0 3 16.3 if 20 0 6
September
: 22 30 25 Left 24 1 0 0 3 69.2 0 0 17 8
9/22-0..... 4 23 30 20 Left 20 0 0 0 0 57.5 0 7 13 0
24 45 20 Left 20 0 0 0 1 68.0 0 u 9 0
25 25-45 20 Left 20 0 0 0 0 69.0 0 10 10 0
September
: 22 30 25 Right 25 0 0 1 0 82.0 0 ll 14 0
23 30 20 Right 15 2 3 0 0 19.0 11 8 0 1
24 40-45 20 Right 20 0 0 0 0 43.0 0 20 0 0
9/22-d..... { 25 20-42 20 Right 20 0 0 1 0 68.0 0 20 0 0
26 28-45 20 Right 0 0 20 0 0 20 0 0 0
27 18-45 22 Right 21 1 0 1 0 44.0 0 21 0 1
29 18-45 2 Right 20 0 0 0 0 48.0 0 20 0 0
30 | 23-45 10 Right 5 5 0 0 0 0 10 0 0
October
2 23-45 22 Right 22 0 0 0 0 71.0 0 13 5 4
3 25-45 20 Right 20 0 0 1 6 73.0 0 4 7 9
1O/d-0, 25 -.,- 4 18-45 23 Right 22 1 0 0 0 68.0 0 13 7 3
5 15-45 21 Right 21 0 0 0 0 68.0 1 15 4 1
6 13-78 22 Right 14 6 2 0 0 27.0 5 13 1 3
7 20-80 24 Right 19 5 0 0 0 43.0 0 23 0 1
July
ot 30 36 Left 32 1 3 0 0 26.5 4 23 5 4
22 20-28 35 Left 23 11 1 0 0 65.0 2 27 3 3
7/21-6..... | 23 28 31 Left 16 13 2 0 0 47.0 4 11 6 10
24 20-28 13 Left 13 0 0 0 0 56.5 0 8 2 3
| 25 28 14 Left 13 0 1 0 0 64.5 1 7 3 3
l 26 28 11 Left 10 0 1 0 0 58.0 0 0 4 7
July |
24 30 10 Left 10 0 0 0 0 28.0 0 10 0 0
7/24-4..... 25 30 11 Left ll 0 0 0 0 35.0 0 ll 0 0
26 30 nb Left il 0 0 0 0 33.0 0 ll 0 0
27 30 11 Left Il 0 0 0 0 0 10 0 1
September
24 30-60 50 Left 39 7 4 7 17 59.0 9 10 1 30
0/24-a..... 4 25 25-60 20 Left 19 if 0 0 0 79.0 0 14 5 1
26 25-45 31 Left 30 0 1 9 3 77.0 1 16 9 5
27 23-45 20 Left 20 0 0 5 6 64.0 0 10 4 6
July
23 30 11 Left 11 0 0 0 0 29.3 0 11 0 0
7/28-4...0. 24 30 rT Left 11 0 0 0 0 36.2 0 11 0 0
| 25 30 8 Left 8 0 0 0 0 26.2 0 8 0 0
26 30 ll Left 11 0 0 0 0 31.2 0 10 1 0
July
11 30 51 Right 48 2 1 0 0 31.0 12 ri 17 15
T/l1-4..... 12 30 75 Right 71 0 4 0 0 50.8 7 8 13 47
13 30 32 Right 30 0 2 0 0 37.6 4 14 Ny 13
14 30 30 Right 27 0 3 0 0 52.5 3 4 ll 12
July
5 | 23 30 18 Left 16 2 0 1 0 33.5 4 if 2 5
7/23-40.... 4 24 30 10 Left 10 0 0 0 0 24.5 2 6 0 2
25 30 10 Left 9 1 0 0 0 31.5 0 8 2 0
26 30 10 Left 10 0 0 0 0 37.0 0 8 1 1
July
T/2G-Biasvas'e'ds 29 30 16 Left il 0 5 0 0 20.3 8 8 0 0
July
G/B Deter 16 30 23 Left 23 0 0 0 2 45.6 7 3 0 13
July
7/16-ph...... 16 30 12 Left 11 1 0 0 1 50.8 0 4 2 6
July
7/20-d....0+« 29 30 10 Left 1 1 8 0 0 11.0 8 1 1 0
July
C/20-D saeuln a 29 30 13 Left 7 2 4 0 0 18.0 5 4 2 2
July
7/16-b....% +. 16 30 20 Left 16 0 4 0 1 27.2 4 14 2 C)
July
7/16-0.5 eee 16 30 18 Left 0 8 10 0 0 16 1 0 i
July Fi
ih > ee 21 30 11 Left 2 5 4 0 0 6.0 7 4 0 0
July
TYAS 2, wis 22 30 4 Left 22 0 2 0 1 34.0 | 8 9 3 4
July
T/Nadis occu 21 30 61 Left 56 1 4 5 18 12 17 2 30
July
T/18-p... 2.0 16 30 17 Left 17 0 0 0 1 38.0 2 4 1 0
July
7/16-e....... 16 30 15 Left 15 0 0 0 0 38.2 0 9 0 6
July
1/15-2..... 15 30 21 Left 20 0 1 0 1 33.5 1 20 0 0
16 30 27 Left 7 8 2 0 0 20.9 16 2 6
Wee ted 30 56 Left at v o a 28 3 8 6 39
7/16-a aoe ve 30 3 Left AON a2 d ¥ 0 g8 | 2B 0 | 10
10/8-Big. aoe et: 20-78 25 Right 25 0 0 1 3 68.0 0 8 5 12
[An St...
Total Lee 3077 2699 207 Wi | 477 204 287 | 1619 493 678
REACTIONS TO LIGHT IN VANESSA ANTIOPA 381
said to have oriented in the ‘shaded region.’ When orientation
occurred either precisely at the edge of the beam or within one
centimeter beyond the edge it is considered to have occurred
‘near the edge of the beam.’ In those trials in which the insect
either continued to perform circus movements or passed on out-
side the beam into the shaded region beyond, in a more or less
straight course with no turn toward the source of light, ‘no
orientation’ is said to have occurred.
An examination of this table shows that out of a total of 3077
trials the butterflies turned toward the functional eye in 2699
trials, and away from it in 207 trials, while in 171 trials they
Fig. 7 Reproduction of 33 successive trails made by butterfly 10/14-b (left
eye blackened) on the first day of the tests. a and b, limits of horizontal beam
of light; 1-33, paths made in successive trials; small arrows, direction of move-
ment of animal; large arrows, direction of rays of light; illumination at z, 1510
mec.; at y, 250 mc. Note that this insect modified its behavior in that it per-
formed circus movements in 13 out of the first 16 trials, but made circus move-
ments in only 6 of the next 16 trials.
moved toward the glower without first turning toward one side
or the other. This indicates clearly that there is in Vanessa
with one eye blinded a strong tendency to turn toward the func-
tional eye.
The table shows aiso that in 2399 of the 3077 trials individuals
with but one functional eye oriented and moved fairly directly
toward the light, and that in 287 trials orientation occurred in
the beam of light, indicating strongly that both eyes are not
necessary in this process.
382 WILLIAM L. DOLLEY, JR.
It shows, moreover, that in 16 of the 27 individuals tested on
more than one day orientation occurred in more trials of the last
day than in those of the first, and that in 18 of the 27 individuals
orientation at the edge of the beam occurred more promptly
during the trials on the last day than it did during those on the
first. This is well illustrated by the reactions of butterfly
10/25-a, described in table 1 and in figures 2, 3, and 4.
It shows, furthermore, that in 20 of the 27 individuals circus
movements decreased in number, and that in 20 the average
. angle of deflection was less in the trials of the last day than it,
was in those of the first. Although not shown in table 1, 10 indi-
viduals performed fewer circus movements in the last trials of
the first day of the tests than in the first trials on this day.
This seems to indicate clearly that with practice there is in
Vanessa with but one functional eye improvement in the accuracy
of orientation in three respects, as previously stated: (a) increase
in promptness of orientation, (b) decrease in the number of circus
movements performed, and (c) decrease in the angle of deflection.
If this is true, then it is evident that orientation is not depend-
ent upon the stimulation of both retinas by equal amounts of light
energy. This conclusion is strongly supported by the fact that
in 171 out of 3077 trials the organism with but one functional eye
did not turn either to the right or the left, but moved fairly
directly toward the source of light. It is moreover supported
by the results obtained in observations on: the relation between
the degree of curvature in circus movements and the luminous
intensity, relation between the angle of deflection and the lumin-
ous intensity, and reorientation after changing the direction of
the beam of light. These are discussed in the following para-
graphs.
2. Relation between the degree of curvature in circus movements
and the luminous intensity
According to the ‘continuous action theory’ smaller curves
should be made in the strong light in the beam than are made in
the weak light outside the beam, for the adherents of this theory, ~
as stated above, hold that the tension of the muscles of the legs
REACTIONS TO LIGHT IN VANESSA ANTIOPA 383
on the two sides of the body varies with the relative amount of
light energy received by the two retinas. No such relation,
however, was at all evident in the observations on Vanessa.
Curves of the same size were made in both positions, and very
frequently those in the region of low illumination outside the
beam were smaller than those in the region of comparatively
high illumination in the beam. This is well seen in the ninth
trial made by animal 10/14-b on the third day (fig. 8). In this
case the butterfly, while in the beam, began to perform a circus
movement of a diameter of 6.5 cm. By the time it was half
Fig. 8 Reproduction of 21 successive trails made by butterfly 10/14-b (left
eye blackened) on the third day of the tests. a and b, limits of horizontal beam
of light; 1-21, paths made in successive trials; small arrows, direction of move-
ment of animal; large arrows, direction of rays of light; illumination at x, 1510
mc.; at y,250mc. Note that in trial 9 this insect turned very much more sharply
toward the functional eye while in the shaded region to the right of the beam than
it did while in the comparatively strong light in the beam.
completed the animal was 3 cm. beyond the edge, and in the
weak light to the right of it. On reaching this point, the insect
turned sharply to the right, and made another circus movement
of a diameter of only 1.5 cm. ie., in weak light the organism
turned more sharply toward the functional eye than in strong.
Similar reactions were observed in many other cases.
3. Relation between the angle of deflection and the luminous intensity
a. Effect of beginning the trials in different intensities. It has
been shown that in those trials before the Nernst glower in which
circus movements are not performed continually, Vanessa antiopa
384 WILLIAM L. DOLLEY, JR.
usually turns until it assumes a certain angle with the rays of
light, and that it then proceeds diagonally across the beam. If
orientation is dependent upon the relative amount of light energy
received by the two eyes, as demanded by the ‘continuous action
theory,’ the degree of deflection ought to be greater in high
illumination than in low, for if only one eye is functional, the
greater the intensity, the greater the difference in the amount
of energy received by the two eyes. This was tested by measur-
ing the angles of deflection in different intensities of light in each
one of the trials made by all of the insects. The results of some
of these tests are recorded in figure 9 and in table 2.
TABLE 2
Angles of deflection made in different intensities of light by four butterflies with one
eye blackened
5 BUTTERFLY 9/22-a BUTTERFLY 10/1-3-b BUTTERFLY 10/8-a BUTTERFLY 10/1-4-b
B | egee jal ees i |eere | 2 7 eeeeue
e\ScF_| 3 |Se28_| = |Sect.| = |Sec8.| §
sped OH od q Ok wo q OR ah Og a
Be Bs aee| #3 | $2 EE EE oe EE gs S525 P| #3
1 380 50 257 80 234 85 234 50
2 380 85 383 80 445 110 275 30
3 624 50 758 50 445 90 624 55
4 2153 60 758 70 624 85 234 30
5 380 95 ‘791 40 275 80 234 30
6 448 65 936 50 791 70 634 50
7 624 50 234 40 383 70 634 50
8 1223 50 337 40 1044 70 936 95
9 2153 65 624 35 218 50 257 90
10 380 75 936 50 234 85 337 90
11 448 80 257 50 257 85 416 75
12 624 60 314 60 634 70 234 100
13 839 65 416 60 291 70 337 80
14 1497 55 624 50 1044 70 624 85
15 2883 80 936 45 416 60 936 _ 110
16 380 65 257 65 234 60
17 547 80 337 45 624 50
18 624 75 624 35 259 60
19 711 80 257 110 1044 50
REACTIONS TO LIGHT IN VANESSA ANTIOPA 385
By referring to this figure, which represents the course of a
given individual in different intensities of light it will be seen
that the angle of deflection is essentially the same in all, in spite
of the fact that the illumination varied from 76 to 3397 me.
This is a typical case. It seems to show that the degree of
deflection is within wide limits independent of the intensity of
the light.
Fig. 9 Diagram showing the angles of deflection made by butterfly 10/8-b
(left eye blackened) when exposed in light of different intensities. A A, limits
of horizontal beam of light; 14-25, successive trials; 76 and 3397, intensity of light
in meter candles at the corresponding points. Note that the insect deflects at
about the same angle with the rays of light, no matter whether the trials are
begun in an intensity of 76 me. or in an intensity of 3397 mc.
The results presented in table 2 support this contention. They
demonstrate that, while the degree of deflection varies greatly
in different individuals and in the same individual under different
conditions, there is no apparent correlation between it and the
intensity of the light. Since the degree of deflection is a measure
of the difference in tension of the muscles of the legs on the two
sides of the body these results also show that there is no apparent
correlation between this difference in tension and the intensity
386 WILLIAM L. DOLLEY, JR.
of the ight. This conclusion receives still further support from
the results obtained in non-directive light which are reserved for
discussion later. Before entering upon further discussion based
on table 2 we will describe experiments as to the effect upon
behavior of changes of intensity.
b. Effect of sudden changes of intensity on the ek of deflection.
The previous experiment in which the position of the glower was |
unchanged, but in which the intensity of the light varied in
different trials was supplemented by others. In some of these
the light was increased after the butterflies had oriented. In
others it was suddenly decreased. The insects with only one
eye functional were placed in a beam of light, and, as soon as
TABLE 3
Effect upon the angle of deflection of suddenly increasing the illumination from 104
mc. to 1400 mc.
NUMBER OF NUMBER OF NUMBER OF
DESIGNATION OF TRIALS IN WHICH TRIALS IN WHICH TRIALS IN WHICH
BUTTERFLIES ANGLES WERE ANGLES WERE NO EFFECT WAS
INCREASED DECREASED EVIDENT
10/2021 <a. 4) eee 5
LOVG=9=b', vanced eae Cee s 2 8
LOU S= Cian isc co ae ee eee 8 1 3
10/3 =0-8) o)..e ee 1 1
LO f=7<c ls. eee eee 5 3
otal... 21 4 15
they had assumed a definite direction of locomotion, the glower
was suddenly moved closer to the organisms, or was suddenly
moved further away. In this way the intensity of the light was
suddenly changed from 104 me. to 1400 me. and vice versa.
Some butterflies turned suddenly toward the functional eye,
others turned toward the blinded eye, and still others did not
respond. The reactions of the animals to sudden increase of
intensity are given in table 3; those to a sudden decrease of
intensity in table 4.
Table 3 shows that in 21 out of 41 trials, the insects nme
ately turned toward the functional eye when the light was sud-
denly increased; that in 4 they turned toward the blinded side;
and that in 15 there was no response.
REACTIONS TO LIGHT IN VANESSA ANTIOPA 387
Table 4 shows that four butterflies were tested, making 23
trials in all, and that in 12 of these there was no response, while
in 8 the butterflies turned toward the blackened eye, and in 3
toward the functional eye.
The results recorded in these two tables show clearly that a
sudden increase of intensity tends to cause the butterflies to turn
sharply toward the functional eye and that a sudden decrease
tends to cause them to turn in the opposite direction.
The reactions, as described above, upon a sudden change in
the intensity of the light are very puzzling until the behavior of
the individual animals is carefully examined. In one of the
butterflies, 10/8-c, whose reactions are given in table 3 and in
TABLE 4
Effect upon the angle of deflection of suddenly decreasing the illumination from 1400
mc. to 104 mc.
NUMBER OF NUMBER OF NUMBER OF
DESIGNATION OF TRIALS IN WHICH TRIALS IN WHICH TRIALS IN WHICH
BUTTERFLY ANGLES WERE ANGLES WERE THERE WAS
INCREASED DECREASED NO APPARENT EFFECT
1 4 4
1 2
2
1 +
+ 2
3 | 8 12
figure 10, the angle of deflection did not change in three trials,
but in seven out of the other nine trials made, it increased, at
once, when the intensity was suddenly increased. Immediately
afterwards, however, as shown in figure 10, the organism turned
toward the glower, and deflected at a smaller angle with the rays of
light than it hud before the intensity had been increased. In one
trial, though, at the sudden increase of intensity, it decreased
the angle, and deflected only slightly in the bean. In another
trial it increased the angle and went out of the beam. °
The behavior of this last animal gives, I think, the clue to
the explanation of the fact that when the intensity of the light is
suddenly changed the angle of deflection decreases in some ani-
mals, while in others it increases. The fact that this butterfly
388 WILLIAM L. DOLLEY, JR.
(fig. 10) increased the angle of deflection at the sudden change
of intensity, and then immediately decreased the angle of deflection,
although the insect was closer to the glower, is very significant
in showing that it is not the higher intensity which caused the
increase in the angle of deflection, but that it is the sudden change
from a lower to a higher intensity. Consequently, the sudden
increase in the angle of deflection that occurs in some cases, seems
A
A\ cl bb *oiB Bl bl le ‘lie mle iF f
“ay y (
A i
gt [ASle# mal high nat Wills Ji 5! letgi« Kiel Mo 4in Lb
t
Fig. 10 Semi-diagrammatic reproduction of the records made by butterfly
10/8-c (left eye blackened) when the illumination was suddenly increased from
104 mc. to 1400 mc. The individual trials are numbered. The limits of the
beams of high intensity are designated by the capital letters; the beams of low
intensity by the small letters. X, position of the animal at the time the illumi-
nation was changed; arrows, direction of movement of animal. Note that the
insect usually turned sharply toward the functional eye immediately after the
illumination was increased, and later again in the opposite direction.
to be a shock reaction and not the result of unequal amounts
of light energy received by the two retinas, as is demanded by
the ‘continuous action theory’ of orientation. Furthermore,
according to this theory the angle of deflection should be-greater
in high than in low intensity. This was, however, not found to
be true, as is shown in table 2 and figure 9. By referring to this
table it will be seen that the angle of deflection in 2000 me.
and in 200 me. was essentially the same, whereas, according to
REACTIONS TO LIGHT IN VANESSA ANTIOPA 389
the ‘continuous action theory’ it should be ten times greater in
the former intensity than in the latter. Moreover, this theory
is not supported by the results obtained when the illumination
is gradually increased after the animals have become oriented in
a beam of light. The condition mentioned is fulfilled in the
experiments already described in which the insects with one
functional eye were tested in a beam from a stationary glower.
In figures 4 and 9 it can be seen that after the butterflies had
become oriented and were moving toward the source of light
at a definite angle with the rays they were gradually approaching
the glower and consequently the illumination was at the same
time being gradually increased. On the basis of the ‘continuous
action theory,’ one would expect the butterflies while in the beam
to curve gradually toward the functional eye, increasing the angle
of curvature as they approached the glower. On the contrary,
they moved while in the beam in fairly straight courses, and the
angle of deflection remained practically unchanged as the organ-
isms drew nearer to the source of light.
This work shows conclusively that the angle of deflection does
not vary with the intensity of the light, thus indicating most
strongly that orientation in Vanessa is not necessarily dependent
upon the relative amounts of light energy received by the retinas.
It also seems to show that the assumption that the tension of
the muscles controlled by the two retinas varies with the amount
of light energy received, does not hold. This conclusion is further
supported by the fact that Vanessa with only one eye functional
can reorient toward either side and so follow a source of light
as its position is changed, as is shown in the following section.
4. Reorientation after changing the direction of the beam of light
To ascertain whether or not butterflies with but one func-
tional eye can reorient they were placed into a horizontal beam of
light and after they had assumed a definite axial position and were
moving toward the source of light at a definite angle to the direc-
tion of the rays, as previously described, the source was moved _
to a second position at the same distance from the animal, but
390 WILLIAM L. DOLLEY, JR.
such that the rays of light were now at right angles to their
former direction. When this was done, it was found that the
butterflies usually reoriented. That is, they usually turned until
they again assumed the same axial position with reference to the
direction of the rays of light that they had taken before the glower
was moved. This occurred no matter if the glower was moved
to the right or to the left. Thus, it is evident that in the process
of reorientation the animals may turn either toward the blinded
or the functional eye (figs. 11 and 12).
Thirty-one butterflies were used in this experiment, and it
was found that, of these, twenty-two reoriented both to the right
and to the left. Nine, however, although they reoriented toward
the functional eye, did not turn toward the blackened eye.
Three of these were kept and tested for several successive days.
The behavior shown in these tests is recorded in table 5.
These results show clearly that Vanessa with only one eye
functional can reorient, and in this process can turn either toward
the blinded eye or toward the functional eye. They also show
that the behavior may become modified since those insects that
do not reorient by turning toward the blinded eye when first
tested are able to do so after a certain amount of experience
(fig. 12, 1-3). Moreover they seem to support the conclusion
derived from results described previously that the performance
of circus movements seems to be favored by a sudden change in
light conditions, since in four of the trials described in table 6
the butterflies either performed circus movements, or apparently
began to perform them, when the position of the glower was
suddenly changed.
The ability of the butterflies with only one eye functioning to
reorient, and so follow the source of light as its position is changed
is important in a consideration of the factors in the process of
orientation. It has a direct bearing on whether or not orienta-
tion in light is dependent upon stimulation of symmetrically
located photosensitive areas, as demanded by Loeb’s theory of
orientation. In reorientation, such as has been described, only
one retina is affected by light. The chemical changes taking
place in the two photosensitive areas are not at all identical.
REACTIONS TO LIGHT IN VANESSA ANTIOPA
TABLE 5
391
Behavior of three butterflies tested for reorientation on several successive days
DESIGNATION| OF DAYS |NUMERICAL
OF
BUTTERFLIES
10/21-b....
NU MERICAL
ORDER
ON WhICH
TESTS
WERE
GIVEN,
1
bo
BEHAVIOR WHEN GLOWER
BEHAVIOR WHEN GLOWER
ORDER WAS MOVED TO THE SIDE OF | WAS MOVED TO THE SIDE OF
OF TRIALS THE COVERED EYE THE FUNCTIONAL EYE
1 Circus movement toward | Reoriented
functional! eye, followed by
movement toward glower
, Circus movement ] Reoriented (See fig. 12, 4)
toward functional
eye, followed by
movement toward
glowe1 See fig-
2 Circus movement } ure12,| Reoriented
toward functional 1-3
eye, followed by
movement toward
glower
3 Reoriented J Reoriented
1 Failed to reorient Reoriented
2 Failed to reorient Reoriented
=) Reoriented Reoriented
4 Reoriented Reoriented
1 Reoriented Reoriented
2 Reoriented Reoriented
1 Failed to reorient Reoriented
2 Failed to reorient Reoriented
3 Failed to reorient Reoriented
4 Failed to reorient Reoriented
5 Failed to reorient Reoriented
6 Reoriented Reoriented
1 Reoriented Reoriented
1 Reoriented Reoriented; immediately per-
formed circus movement to-
ward functional eye; then
went toward glower
1 Reoriented Reoriented
1 Circus movement toward | Reoriented
10/24-a.... 4
functional eye, followed by
movement toward glower
Sharp turn toward functional
eye as if to make circus, but
turned and moved toward
glower
Behavior similar to that shown
when glower was moved to
side of covered eye
392 WILLIAM L. DOLLEY, JR.
The organism is non-symmetrical, only one eye being functional.
And yet the butterfly moves toward a source of light, deflecting,
it is true, toward the functional eye, and when the position of
the light is changed, the animal also changes the direction of its
motion to correspond with the change in position of the source
of light. This behavior bears little resemblance to that which
would be exhibited were the organism such that it could only
Fig. 11 Reproduction of trails made by four butterflies showing reorientation.
Large arrows, A and B, direction of rays of light in the two positions of the
glower; small arrows, direction of movement of the butterflies; x, position of
animals when the direction of the rays was changed; 1 and 2, trails made by butter-
fly 7/29-d; (left eye blackened); 3 and 4, trails made by butterfly 7/16-c (left eye
blackened); 5 and 6, trails made by butterfly 7/29-b (left eye blackened); 7 and
8, trails made by butterfly 9/22-b (right eye blackened).
REACTIONS TO LIGHT IN VANESSA ANTIOPA 399
results secured by Hadley with larval lobsters. He found that
these animals, at all ages, moved in circles toward the blinded eye,
although they vary in the sign of their reaction to light at differ-
ent ages. He says (08, p. 197): ‘‘In the lobster larvae all the
progressive reactions which took place immediately following the
blinding of one eye were positive. In certain cases it appeared
that either the operation itself, or the effects of blinding changed
the index of reaction from negative to positive. In all these
instances, whether the previous reaction had been negative or
positive, the resulting behavior was the same; a series of revo-
lutions, or circus movements, or a progression in which the direc-
tion of turning indicated that the influence of light on the
unblackened eye was to cause greater activity of the swimming
appendages on that side of the body, while blinding invariably
had the opposite effect. In other words, the reaction of. the
blinded positively reacting lobster larvae corresponds with those
of Holmes’s negatively reacting amphipod, Hyalella dentata
(Smith) but not with his positively reacting amphipods.”
Hadley is the only investigator who records continuous move-
ments only toward the non-functional eye in individuals both in
the positive and in the negative state. It is therefore probable
that the circus movements described by him were due not to the
withdrawal of the light stimulus from one eye, but to the stimu-
lation produced by searing the eye with a hot needle, which was
the method used by him in blinding his animals. These experi-
ments ought to be repeated and the organisms tested on succeed-
ing days. Besides, this method of blinding the lobster should
be supplemented by entirely cutting off the eye stalk and testing
for several days in succession the young lobsters so operated on,
‘thus eliminating the possible effect of injury on the response.
D. BEHAVIOR IN NON-DIRECTIVE LIGHT
In the preceding pages we have discussed the behavior of
Vanessa in a horizontal beam of light, and in the absence of light.
We shall now describe its reactions in a field uniformly illumi-
nated from above. When the butterflies are placed in a beam
of light, all of the light that reaches them emanates practically
400 WILLIAM L. DOLLEY, JR.
from one point, so that the illumination of the functional eye
varies with every change in position of the animals. The ques-
tion naturally arises as to whether or not many of the reactions
observed under these conditions are due to this change in the
illumination. This was settled conclusively by placing the butter-
flies with one eye blackened in light so arranged that the illumi-
nation of all of the large portions of the uncovered eye was
essentially the same in all of the positions assumed by the insects,
i.e., in which the light was non-directive.
To accomplish this the box described in the preceding section
was used. Over the top of the box there was drawn an opaque
cloth cover, in the center of which a circular hole, 3 cm. in
diameter, was cut. A 16 ¢.p. electric lamp was placed directly
over this hole in contact with the cloth. The butterfly was then
Fig. 16 Reproduction of trail in non-directive light, 6 mc., made by butterfly
7/16-c (right eye blackened) immediately after the eye was covered. Note the
continuous turning toward the functional eye.
placed upon the papers in the bottom of the enclosure. Some
light was reflected from the sides and bottom of the black box,
but the amount of this reflected light was comparatively very
small, and, moreover, it was approximately equal on all sides of
the animal. The luminous intensity at the bottom of the box
was 6 me. ;
Thirty-one butterflies were tested in this apparatus in non-
directive light soon after one eye had been blackened, and nine
were also given trials on several successive days. The behavior
exhibited by these animals is recorded in figures 16 and 17 and
in table 6.
A study of this table and the figures show that if Vanessa
antiopa with one eye blackened is placed in non-directive light
it tends to turn continuously toward the functional eye, and that
REACTIONS TO LIGHT IN VANESSA ANTIOPA 397
to the contact stimulus exerted by the covering of the blackened
eye, for in light the insects turn toward the functional eye. It
seems to demonstrate, moreover, that there is but little, if any,
permanent modification in the behavior on successive days, for
essentially similar reactions were observed in all of the insects
during the whole period over which the tests extended.
Fig. 15 Reproduction of trails in total darkness made by butterfly 7/11 (right
eye blackened) in ten successive trials forty-eight hours after the eye had been
covered. Compare the preceding figure with this one, and note that in the tests
on three successive days this butterfly usually turned continuously toward the
blackened eye, showing little, if any, modification in behavior.
The results obtained in these experiments throw light on the
puzzling results which Holmes and McGraw obtained in their
experiments with butterflies. They used a jar, the bottom and
sides of which were lined with white paper. This was covered
by a cone of the same material, and at the apex of this cone,
an electric light was placed. When butterflies with one eye
398 WILLIAM L. DOLLEY, JR.
blackened were placed in the center of the enclosure, specimens
of some species went uniformly in circles toward the uncovered
eye, while those of other species, among them Vanessa antiopa,
moved continuously toward the blinded eye, although all were
positive. Since insects which are positive in their reactions to
light usually go in circles toward the uncovered eye, when one
eye is blackened, while those which are negative go in circles
toward the blackened eye, the above results were apparently
inexplicable. Since, however, Vanessa antiopa, which is highly
positive, goes in darkness in circles toward the blinded eye, it
is clear that the results secured by Holmes and McGraw are to
be explained by the fact that at times the stimulus exerted by the
covering of the eye was strong enough to overcome the stimulus
exerted by light on the uncovered eye. When the butterflies went
toward the functioning eye, they were responding to light, while
when they went in circles toward the blinded eye they were re-
sponding to the stimulus exerted by the covering of the blackened
eye.
The above statement probably applies equally well to the
peculiar results which Brundin obtained. These are described
in the following.manner (13).
“Tn positive specimens of Orchestia traskiana, circus move-
ments will occur as often toward the blackened eye as toward
the normal eye. All specimens used for this experiment were
strongly positive. There is no way to account for this varia-
bility, except that the animal might be made temporarily nega-
tive by having one of the eyes covered over. The fact, however,
that as soon as the blackening is removed from the eye of one
of these ‘apparently negative’ specimens, its reactions to the
light is decidedly positive, seems to throw considerable doubt
upon this hypothesis.”
It seems very probable that the circus movements toward the
blackened eye performed by this amphipod were due to a stimulus
produced by the covering of the blinded eye and were not due
to light.
It is possible, also, that the above described behavior in dark-
ness of Vanessa may be suggestive in connection with the peculiar
REACTIONS TO LIGHT IN VANESSA ANTIOPA 395
This general statement of the behavior is illustrated by the
following detailed description of the reactions of two insects.
1. Butterfly 7/16-c (right eye blackened) was tested in dark-
ness ten hours after the eye had been covered. It moved con-
tinually toward the blinded eye (fig. 13).
2. Butterfly 7/11 (right eye blackened) was tested immedi-
ately after the eye had been covered and again on each of the
following two days. In the first trial it turned continuously
toward the blackened eye. In the second and third it went in
straighter courses, but showed a decided tendency to curve to
Fig. 13 Reproduction of tracings made in total darkness by butterfly 7/16-c
(right eye blackened) showing continuous turning toward the blackened eye.
Arrows indicate direction of movement. This record was made ten hours after
the eye was covered.
the right (fig. 14, A). On the second day three trials also were
given, and in each of these the organism turned continuously
toward the blackened eye (fig. 14, B). On the third day in the
first five of the ten trials given this insect again turned continu-
ously toward the blinded eye, and in. the other five it deflected
in the same direction, but not so strongly as in the first five
trials (fig. 15). It can thus be seen that the behavior exhibited
on the first day was, in general, retained on the succeeding days
of the tests.
- Similar results were obtained in observations on a number of
other specimens. These may be summarized as follows: Eight
butterflies were tested for ten minutes each day for ten consecu-
396 WILLIAM L. DOLLEY, JR.
tive days; three for four days; three for three days; one for two
days; and thirteen on only one day. All of these animals usually
turned continuously toward the blackened eye.’ The behavior
was strikingly uniform. This continuous movement toward the
Fig. 14 Reproduction of trails made by butterfly 7/11 in total darkness (right
eye blackened). A, 1-3, trails made in three successive trials immediately after
the eye had been covered. B, 1-3, trails made in three successive trials twenty-
four hours later.
blackened eye under conditions in which no light can affect the
uncovered eye shows conclusively that the covering of the eye
exerts a stimulus of some sort upon the organism. It also shows
that the deflection toward the functional eye in light is not due
REACTIONS TO LIGHT IN VANESSA ANTIOPA 393
orient if both eyes were stimulated equally. Were this hypothe-
sis true, the animal with only one eye functional could not orient,
Fig. 12 Reproduction of trails made by three butterflies showing reorienta-
tion. Large arrows, A and B,-direction of rays of light in the two positions of
the glower; small arrows, direction of movement of the butterflies; x, position of
the animals when the direction of the rays was changed; 1-4, trails made by butter-
fly 7/4 (right eye blackened) ; 5-6, trails made by butterfly 10/21-b (left eye black-
ened); 7-8, trails made by butterfly 10/24-a (right eye blackened). Note that
butterfly 7/4 (right eye blackened) failed to reorient promptly toward the side
of the blackened eye in the first two trials, but that in the third it did reorient
promptly in this direction, showing marked modification in behavior. This figure
and the preceding one are presented not merely to show the accuracy with which
Vanessa, with only one eye functional, reorients upon change in position of the
source of light, but also to show some of the peculiarities exhibited by different
individuals.
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3
394 WILLIAM L. DOLLEY, JR.
but would be compelled to perform circus movements continu-
ally, regardless of the position of the source of light.
This experiment, however, throws no light on the nature of
the stimulus effective in orientation. Reorientation could con-
ceivably occur in organisms with but one functional eye, whether
light exerts its orienting stimulus through its continuous action,
as demanded by the ‘continuous action theory,’ or througha
change of intensity, as demanded by the ‘change of intensity
theory.’ ;
C. EFFECT OF THE COVERING OF THE EYE OWING TO CONTACT
We have clearly demonstrated that Vanessa with but one
functional eye tends to turn toward this eye when it is placed
in a beam of light, and that this tendency decreases with experi-
ence. Are these responses due to the elimination of the action
of light on the blinded eye or to the effect of the contact of the
covering on this eye? This question was answered very con-
clusively by placing in darkness specimens with one eye covered.
In this experiment a wooden box (45 x 55 x 59 cm.) lined with
black cloth was used. In the bottom of this box were placed
sheets of paper covered with soot. The butterfly to be tested
was placed in the enclosure upon the sheets of paper, and an
opaque cover was drawn over the top of the apparatus. All the
experiments were performed in the dark room, many of them
late at night. The precautions taken were of such a nature that -
the observer feels confident that no light could possibly have
reached the organisms.
Under these conditions it was found that the animals made
circus movements, but in the reverse direction from that in
which they moved in the presence of light. With few exceptions,
the butterflies turned continuously toward the blinded eye, and in
most of the exceptional cases they showed a decided tendency to
curve somewhat in this direction. Only in a few cases did they
move in a straight line. In some of these the course was nearly
straight for eight or ten centimeters or more.
TABLE 7
Showing the relative degree of curvature between the circus movements made in non-
directive light of low intensity and those made in that of high intensity
407
(a paeerieae NON-DIRECTIVE LIGHT OF AN NON-DIRECTIVE LIGHT OF AN
BUTTERFLIES INTENSITY OF 2 MC, INTENSITY OF 460 mc.
9/22-c Circus movements Fairly straight courses with a de-
cided curve toward uncovered
eye
9/22-b Circus movements Circus movements with larger
angles of curvature
9/21-a Circus movements Circus movements with slightly
larger angles of curvature
9/22-d Similar circus movements
10/1-a Circus movements Circus movements with much
larger angles of curvature
10/1-b Fairly straight courses although | Fairly straight courses with nu-
circus movements are made merous turns toward the black-
ened eye
10/1-c Fairly straight courses in fifteen | Fairly straight courses in fifteen
trials trials
Under both conditions a decided tendency to turn toward the func-
tional eye though numerous turns are made toward the black-
ened eye
10/1-c-6 Circus movements in both cases—records indistinguishable
10/13-a Circus movements Circus movements with much
larger angles of curvature
10/14-18-a | Fairly straight courses under both conditions
10/16-a Trials indistinguishable
10/20-a Circus movements Circus movements with much
larger angles of curvature
10/21-b Circus movements: Circus movements with slightly
larger angles of curvature
10/24-a Circus movements Circus movements with slightly
larger angles of curvature
* 10/28-a Circus movements in both cases—records indistinguishable
10/31-a Circus movements Straightened courses
408 WILLIAM L. DOLLEY, JR.
fairly straight courses with a decided curve toward the uncovered
eye. In the case of seven individuals the trials made in the two
conditions of illumination were indistinguishable.
In table 8 are given the results obtained when non-directive
light of a very low intensity was used.
TABLE 8
Amount of decrease in intensity of non-directive light necessary to force the bulter-
flies to cease making circus movements toward the functional eye and to make
circus movements in the-opposite direction
ESE es THE DIRECTION OF THE Ce tee as eae CIRCLES TOWARD THE
UNCOVERED EYE BLINDED BYE
0.24 me. 0.09 me. 0.0265 me.
23 0.15 me 0.1 me. 0.265 me.
0.043 me.
3 0.52 me. 0.4 me. 0.18 me.
0.273 me.
4 0.114 me. 0.47 me.
0.036 me. 0.025 me.
ix 0.077 me. 0.046 me.
0.014 me. 0.011 me.
This table shows, in general, that the animals placed in non-
directive light of low intensity, half a meter-candle or less, make
circus movements toward the functional eye; that if the inten-
sity of the light is then decreased, the insects deflect less and
less until their courses become relatively straight; and that if
the intensity is then still further decreased, they move in ‘circles’
‘toward the blackened eye.
It must be concluded from these reactions that it is probably
true that in light below certain limits, the effect of*the light
and that of the covering of the eye, may become equal. But, if
this is true, it does not necessarily mean that the nature of the
stimulus produced by the contact of the covering with the eye
and that caused by light in the opposite eye is the same. It is
possible that while the covering probably stimulates through its —
continuous action, light may stimulate by virtue of change of
intensity. ‘This may well be so, and yet the effect of the two
REACTIONS TO LIGHT IN VANESSA ANTIOPA 405
light was reduced to 2 me. The higher intensity was produced
by replacing the 16 c.p. lamp with two Nernst filaments side by
side. The luminous intensity produced in this way was 460
me. ‘The insects were tested first in the light of low intensity,
and then in that of high intensity. They were kept in darkness
for twenty minutes before being exposed to either of these two
lights. In the second experiment a white sheet of paper measur-
ing 20x 17 cm. fastened over a piece of board of the same size,
was placed above the center of the box at an angle of forty-five
degrees with the plane of the bottom. A horizontal beam of
light from a Nernst glower was thrown on this sheet of paper,
and reflected into the box below. By altering the elevation of
the reflecting surface, and also by varying the distance between
the glower and this surface, the intensity of the light in the box
could be changed. In this way light of very low intensity was
produced.
The results obtained in these experiments may be illustrated
by a description of the behavior of two animals.
Butterfly, 10/13-a (left eye blackened), after having been in
darkness twenty minutes, was exposed to non-directive light of
an intensity of 2 me. It made four circus movements, turning
continuously toward the functional eye, and then stopped. It
was picked up and dropped a second time, on the smoked papers
in the bottom of the box. In this, the second trial, it again per-
formed circus movements in the same direction. Similar reac-
tions were observed in all the rest of the ten trials made (fig. 18).
After a stay of twenty minutes in darkness, the source of light
of high intensity was used, and the insect was given ten trials.
In all of these it either made circus movements in the same direc-
tion as in the lower intensity, with a much smaller degree of
curvature, or walked in fairly straight courses, as is shown in
figure 19.
Instead of moving in smaller ‘circles’ in light of high intensity
than in that of low intensity, as the ‘continuous action theory’
demands, the organism showed the reverse behavior, for the
smaller ‘circles’ were all made in the lower intensity instead of in
the higher. ;
406 WILLIAM L. DOLLEY, JR.
Butterfly 10/3-a (right eye blackened) was placed in non-
directive light of very low intensity, and this intensity was then
still further decreased. It was found that circus movements
toward the functional eye continued to be performed until the
intensity reached 0.24 me. When it was, however, still further
decreased, the courses became more and more direct, until at 0.09
me. the animal moved in a fairly straight line. When the in-
tensity was lowered still further the butterfly deflected toward
the blackened eye, and when it had reached 0.0265 me. the insect
moved in ‘circles,’ turning toward this eye.
Fig. 18 Reproduction of trails made in non-directive light of low intensity,
2 mce., by butterfly 10/13-a (left eye blackened). Note that the animal moves in
small ‘circles’ continuously toward the functional eye.
The reactions described above are typical of those exhibited
by the twenty-one butterflies exposed to non-directive light of
different intensities, as is shown in tables 7 and 8.
From table 7 it can be seen that out of sixteen animals tested
in non-directive illumination of two intensities, one 230 times
greater than the other, in not a single case did an animal move
in smaller ‘circles’ in the higher than in the lower intensity. On
the contrary, four butterflies actually made much smaller ‘circles’
in the weak light than they did in the strong light, and three
animals made slightly smaller ‘circles’ in the weaker light. More-
over, one insect which made circus movements in the weaker
light did not make any at all in the stronger, but rather went in
REACTIONS TO LIGHT IN VANESSA ANTIOPA 403
eye was functional. But when placed in non-directive light,
essentially the same surface of the functional eye was continu-
ously illuminated; while in a horizontal beam, the surface of the
eye illuminated changed whenever the animal turned in either
direction. The absence of circus movements in the beam of
light must, therefore, have been due in some way to the change
in the illumination of different regions of the eye, produced by
the lateral movements.
This conclusion is further supported by the fact that all of the
animals with one eye blackened used in the experiments de-
scribed in the present paper, if placed before a window per-
formed circus movements continuously, whenever they moved.
In some cases the organisms were kept under these conditions
for as long as two weeks, and frequent observations revealed no
modification in their behavior. Yet when these same insects
were placed in a horizontal beam from a glower they made no
circus movements after a certain amount of experience. When a
butterfly with one eye blackened, is placed before a window, the
light conditions resemble, in many respects, those present in
non-directive light. A change in position on the part of the
organism, does not involve the illumination of an entirely different
area of the functional eye. In every position all large areas of
the eye are approximately equally illuminated, and no two posi-
tions involve the illumination of entirely different areas of the
eye, for the sources of reflected light are countless, and extend
on all sides of the animal.
No definite conclusion can, however, be drawn as to the nature
of the stimulus which regulates the movement of the butterflies
in non-directive light. Superficially it would appear to be due
to the continuous action of light. Yet, it must be remembered,
that with every change in the axial position of the butterfly,
although there may be essentially no change in the illumination
of the surface of the eye, there must be accompanying changes of
intensity upon certain of the ommatidia. ‘There is just one
possible type of reaction in which the same ommatidia would be
illuminated equally in all of the positions assumed by the insect,
and that is movement of the organism in a cirele with its center
404 WILLIAM L. DOLLEY, JR.
directly below the center of the lamp. But since this did not
occur, it is evident that there must be changes of intensity of
light upon certain ommatidia coincident with every change in
position of the head.
The fact that some butterflies with one eye blackened, when
placed in non-directive light, at times moved in a more or less
straight course, especially when tested twenty-four hours or more
after the eye was covered, also demands attention. In these
straightened courses, the movement is either controlled entirely
or in part by internal factors, or it is the result of a balanced
effort of two stimuli; one, light, tending to cause the organism
to turn in one direction, and another, the varnish, tending to
cause it to turn in the opposite direction.
E. RELATION BETWEEN THE DEGREE OF CURVATURE IN CIRCUS
MOVEMENTS AND THE INTENSITY OF NON-DIRECTIVE LIGHT
If the assumptions made by the adherents of the ‘continuous -
action theory’ are valid, i.e., if orientation in organisms is depend-
ent upon the relative amount of light energy received by the two
retinas, and if the tension of the muscles controlled by the retinas
varies with the amount of light energy received, then the circles
made by animals with but one functional eye in non-directive
light of high intensity should have a smaller radius than those
made in light of low intensity, for the amount of light energy
received by the functional eye would be greater in the high in-
tensity than that received in light of low intensity, and, conse-
quently, the inequality between the amounts of energy received
by the two retinas would be greater under the former condition
than under the latter.
This was tested in two experiments. In one, non-directive
light of two fairly high intensities was used; in the other, the
insects were first exposed to light of very low intensity (0.5 to
0.07 me.) and then the intensity was gradually decreased. These
experiments were performed in the light-tight box previously
described. , In the first experiment the lower intensity was pro-
duced by placing a 16 c.p. lamp over the opening of the box, and
by interposing resistance in the circuit until the intensity of this
TABLE 6
Behavior of butterflies with one eye blackened, in non-directive illumination of 6
mc. when tested on several successive days
OF
ANIMALS
(89S Bere &
(701 Ree
!
RA eee a sins.c's
=
a
ne
| ———. SSS ee ao —_N
NUMERICAL
DESIGNATION |ORDER OF DAYS
ON WHICH
TESTS WERE
GIVEN
oe WS dD
ow
BEHAVIOR
Circus movements; circles 6 cm. in diameter; in several trials it went
in more or less straight courses for as muchas 18cm. andthen curved
toward the functional eye
Not tested
Not tested
Continuous circus movements; circles 5 cm. in diameter
Circus movements; circles 15 cm. in diameter; in several trials went
in more or less straight courses for as much as 18 em. and then
curved toward the functional eye
Circus movements; circles 5 cm. in diameter
Circus movements; circles 20 cm. in diameter
Circus movements; circles 5 cm. in diameter; in several trials went
in more or less straight courses for as much as 10 em.
Circus movements; circles 6 em. in diameter; in several trials went in
more or less straight courses for as much as 15 cm.
Circus movements; circles 5 em. in diameter.
Circus movements; circles 5 cm. in diameter, in several trials went
in more or less straight courses for as much as 10 em.
Same behavior as on first day
Circles 8 em. in diameter in direction of blackened eye
Behavior similar to that shown on first day
Circus movements; circles 4 cm. in diameter
Circus movements; circles 3 em. in diameter.
Circus movements; circles 10 cm. and 5 cm. in diameter
No circus movements made; animal moved in more or less straight
courses for as much as 15 and 16 cm. and then stopped, showing,
however, a decided tendency to turn toward the functional eye
Circus movements; circles 10 em. in diameter; in several trials went
more or less straight courses for as much as 15 em.
Circus movements; circles 5 cm. in diameter
Circus movements; circles 3 cm. in diameter, with sharp turns toward
blackened eye also
Circus movements; circles 3 cm. in diameter
Repeated circus movements
Four circus movements; circles 2 cm. in diameter; it then went in two
zig-zag courses, which were each 20 cm. long
Circus movements; circles 2 cm. in diameter
Circus movements; circles 10 cm. and 3 cm. in diameter; nine circus
movements in all; it also made three other trials, in which it went
in a zig-zag course for as much as 45 cm.
Circus movements; circles 3 cm. in diameter; in several trials it went
in more or less straight courses for as muchas 10 cm.
Not tested
Not tested
Circus movements; circles 5 em. in diameter; walked 18 cm. in a more
or less straight course
' 401
402 WILLIAM L. DOLLEY, JR.
this tendency is in general retained for several successive days,
although some modification in reactions is evident. This state-
ment, that there is some change in behavior, is supported by the
fact that of the nine animals tested on more than one day five
continued to perform circus movements on the first day of the
tests, but on succeeding days in some trials went in courses which
were more or less straight for several centimeters.
Fig. 17 Reproduction of trails made in trials on thrée successive days in non-
directive light of 6 mc. by butterfly 7/11-3 (right eye blackened). a, trails made
in three trials on the first day, b, trails made in eight trials on the second day,
c, trails made in six trials on the third day. Note that the insect moved in
rather straight courses on the second day, while on the first and third days it
usually turned continuously toward the functional eye.
From time to time throughout the entire period, the animals
used in the experiment above were tested in a horizontal beam.
In the beginning some of them made circus movements, and
some did not, but at the close of the experiment none of them
made circus movements. This is of great interest, for in non-
directive light these insects continued to make circus movements
throughout the.entire period. Under both conditions, only one
REACTIONS TO LIGHT IN VANESSA ANTIOPA 409
stimuli may be neutralized by their simultaneous action on the
organism.
These experiments in non-directive light of different intensi-
ties show conclusively that there is no relation between the degree
of curvature of circus movements and the intensity of the light
above certain very low limits. They thus support most strongly
the conclusion reached before, that orientation in Vanessa is
not dependent upon the relative amount of light energy received
by the two retinas. ‘
Fig. 19 Reproduction of trails made in non-directive light of high intensity,
460 me., by butterfly 10/13-a (left eye blackened). Compare the preceding figure
with this one and note that in light of high intensity the animal does not move
in courses with a smaller degree of curvature than it does in light of low intensity,
thus exhibiting reactions not in accordance with Loeb’s theory of orientation.
In addition these results contradict an apparently possible
explanation of the reactions in the horizontal beam of light.
Superficially it would seem that these reactions may be due
simply to a balanced effect of two stimuli acting unilaterally,
one, light, acting continuously and tending to cause movement
toward the functional eye, and the other, the covering of the
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3
410 WILLIAM L. DOLLEY, JR.
blackened eye, tending to cause movement toward the non-
functional eye. However, the lack of correspondence between
the size of the circles made and the intensity of non-directive
light shows that the organism does not respond to differences
in intensity as would be demanded by this theory. This con-
clusion is further supported by the fact that a gradual change
in the intensity of light does not affect the angle of deflection.
Consequently orientation can not be due to a balanced effect
of the action of the covering on one eye and the action of light
on the other.
F. EFFECT OF ILLUMINATING ONLY ONE EYE
1. Effect of illuminating the entire surface of one eye
The experiments described previously in which one eye was
thrown out of function by being blackened were supplemented
by others in which one eye was prevented from functioning
simply by not being illuminated. This was accomplished by
methods somewhat similar to those used by Holmes and McGraw
(13). These investigators held insects between the fingers over
a ‘‘thin horizontal dise rotating on a pivot, like the turntable
of the microscopist,’’ with the head pointing either toward or
away from the center. ‘‘An electric light was so placed that
the rays of light fell upon one side of the body. These insects
attempted to turn toward the light, and by the action of their
legs, caused the disc to rotate in the opposite direction. When
the animals became quiet they could, generally, be caused to
resume their activity by pulling them slightly backward.”
Holmes and McGraw draw very decided conclusions from the
results of these experiments. They say (p. 373): ‘“‘There can
be little doubt that light exercised a continuous stimulating
influence upon their [the butterflies] activity. It is not possible,
we believe, to construe phototaxis entirely in terms of differential
sensibility. Responses to the shock of transition, whether in
the direction of an increase or a decrease of stimulus, may play
a part in the orientation of many forms, but the continuous stimu-
lating influence of light appears to be, in several cases, at least,
the factor of major importance.”
REACTIONS TO LIGHT IN VANESSA ANTIOPA 411
Feeling that the methods, as described above, were scarcely
adequate to justify the conclusions drawn, a somewhat similar
piece of apparatus was constructed with the important modifica-
tions that the light conditions were sharply defined, and that the
animals were suspended above the dise by means of a mechanical
holder, instead of being held with the hand. The object of this
experiment was to ascertain the nature of the stimulus effective
in orientation, that is, whether light produces orientation through
its continuous action or through a change of intensity. A way
of determining this would be to exclude one of these possible
methods of stimulation and to test the effect of the other alone.
Consequently, if the latter method is to be excluded, the organ-
ism should be so held that it would be subjected to no changes
of intensity. This condition is met only if the precautions
deseribed above, or similar ones, are taken.
That this condition might be fulfilled and that the direction
of movement of the animal might be detected, a circular piece
of thin black card board, 10 cm. in diameter, was suspended in
a horizontal position by means of a hat pin which was held in a
support that offered as little resistance to the easy movement
of the pin as possible. To the bottom of the dise a thin cork
was glued so that the pin pierced the cork as well as the disc.
The butterflies were suspended above the dise by means of a
holder which clamped the wings firmly together. The holder
was then adjusted so that the insects faced the center of the disc,
and were at such a distance above the disc that they could just
touch it with their feet, and yet not get a firm grip upon it.
A Nernst glower was so situated that the rays from it struck
the right eye of the animal at right angles to the long axis of the
body. By means of sereens the beam of light was made so small
that the area of a cross section of it was but slightly larger than
the surface of the illuminated eye. In line with the glower and
the head of the animal a mirror was so placed that it reflected
the shadow of the head of the animal down upon the table which
supported the whole apparatus, as is shown in figure 20. A screen
was placed around the image so that as little light as possible
might be reflected into the room. Under these conditions the
412 WILLIAM L. DOLLEY, JR.
head, only, was illuminated. Any movement of the legs of the
insect could, however, be instantly detected, for, as the legs
moved the head was ‘bobbed’ simultaneously up and ‘down.
Thus, by observing the reflected shadow of the head, the periods
of activity of the animal could be ascertained.
The results obtained were essentially the same in all of the
seven experiments performed. They may be illustrated by the
following detailed description of part of one of them. After the
Fig.20 Diagram to show apparatus used in experiments in which the butterfly
is suspended above a rotating disk. A, Nernst glower; B, disc; C, butterfly;
D, holder clamped over wings of butterfly; #, mirror.
butterfly was placed in the mechanical holder, with the right
eye illuminated by the beam of light, it remained quiet for 390
seconds; then became active and continued to move for 15
seconds; after which periods of rest and activity alternated as
follows: quiet 240—active 10—quiet 60—active 30—quiet 60—
active 5—quiet 60—active 30—quiet 90—active 5—quiet 60—
active 120. Whenever the insects were active they attempted
REACTIONS TO LIGHT IN VANESSA ANTIOPA 413
to turn toward the functional eye, never in the opposite direc-
tion. What causes changes from rest to activity, and what is
the significance of the fact that the animals attempt continu-
ously to turn toward the functional eye?
During the periods of rest the changes in illumination in the
eyes were exceedingly slight for the light remained practically
constant, and there was no change in the position of the eyes.
Consequently, if the change from rest to activity is due to light
at all, which is questionable, since the butterflies do at times
move in total darkness, it must be due to stimuli dependent upon
the continuous action of light, not upon the time rate of change
in intensity. Regarding the nature of the orienting stimulus
the results are unfortunately not so conclusive, for the moment
the animals become active, and before they attempt to turn,
there is a change in the position of the eye owing to the vertical
movements of the head, and this, no doubt, results in changes
in the luminous intensity on the various ommatidia. Thus, it
is evident that the attempt on the part of the animal to turn
toward the illuminated eye may be due to stimuli dependent
upon the time-rate of change of intensity.
Thus, it is clear that these results do not fully settle the ques-
tion as to how light acts in producing the orienting stimulus and
that the conclusions of Holmes previously stated are not justified.
The method described above of exposing one eye only to light
gives opportunity for testing the effect of illuminating different
areas of the eye. The results of this experiment are presented
in the following section.
2. Effect of illuminating different areas of one eye
We have demonstrated that in Vanessa only one eye is neces-
sary in the process of orientation in light. Now the question
arises concerning the effect of the illumination of different areas
of the eye. If there is any effect then the axial position assumed
by the animal ought to bear some specific relation to the area of
the eye illuminated.
This was tested by suspending the insects above a disc, as in
the previous experiment, and by allowing the horizontal beam
414 WILLIAM L. DOLLEY, JR.
of light to strike the right eye from different directions. In one
experiment the beam struck the eye obliquely from the rear as
is represented by the arrow (a) in figure 21. Thus the posterior
half of the right eye was illuminated while the left eye was in
darkness. In another the rays of light struck the right eye
obliquely from in front, as is represented by arrow (b) in figure
ZA
Under the former conditions, when the posterior half of the
right eye was illuminated, eight animals were tested, each for
thirty minutes. As in the preceding experiment these insects
showed alternate periods of rest and activity. During the periods
of activity they all attempted to turn toward the illuminated
eye, as was shown by the direction in which they revolved the
disc.’
X
Ka
Fig. 21 Diagram to represent the direction from which beams of light were
allowed to strike the right eye (see text).
Under the latter conditions, when the anterior half of the right
eye was illuminated, the animals were also alternately quiet
and active. When active they varied in their behavior. Some
attempted to turn toward the illuminated eye, while others
attempted to turn in the opposite direction. They were tested
on several successive days, the tests on each day lasting for
thirty minutes. |
The first animal (A) tested attempted to turn continuously
toward the shaded eye on the first day. On the second day,
during the first part of the test, it attempted to turn in the same
direction, but during the last part of the test it attempted to
turn in the opposite direction, i.e., toward the illuminated eye.
* The dise could not be seen. Its direction of motion was perceived, however,
by means of a ight paper arrow glued to the bottom of it. The hand of the
observer was so held that the arrow struck the hand as the disc revolved.
REACTIONS TO LIGHT IN VANESSA ANTIOPA
415
On the two following days it continued to attempt to turn
toward the illuminated eye.
The second animal (8) on the first day attempted to turn
toward the shaded eye continuously. On the second day its
behavior varied.
As in the experiments in which one entire
eye was illuminated, this animal without any perceptible change
TABLE 9
Showing direction in which eight butterflies attempted io turn on successive days when
the anterior surface of the right eye was illuminated obliquely from in front
DESIGNATION OF
ANIMALS
B
tc)
F
7
—
ee — eS Se = =
FIRST DAY
Away from il-
luminated
eye
Away from il-
luminated
eye
Toward — illu-
minated eye
Away from il-
SECOND DAY
Away from il-
luminated
eye
Away from 1l-
luminated
eye and to-
ward _ this
eye
Toward | illu-
minated eye
Toward | illu-
luminated| minated eye
eye
Toward illu-| Not tested
minated eye
Toward illu-
minated eye
(Most cases)
Away from il-
luminated
eye at first;
then toward
illuminated
eye
Away from il-
luminated
eye
Toward illu-
minated eye
Away from il-
luminated
eye in most
cases
Toward illu-
minated eye
THIRD DAY
FOURTH DAY
Toward illu-
minated eye
Toward illu-
minated eye
Toward illu-
minated eye
Toward © illu-
minated eye
Not tested
Toward illu-
minated eye
Toward illu-
minated eye
Toward illu-
minated eye
Not tested
Toward illu-
minated eye
Not tested
Not tested
Not tested
Toward illu-
minated eye
Toward illu-
minated eye
Not tested
416 WILLIAM L. DOLLEY, JR.
in the environment exhibited alternate periods of activity and
rest. Forty periods of activity were observed during the test.
In fifteen of the first twenty of these it attempted to turn away
from the illuminated eye, while in fifteen of the last twenty it
attempted to turn in the opposite direction. On the third day
it attempted to turn toward the illuminated eye uniformly.
In table 9 the results secured with the eight animals used in
these tests are summarized. |
By referring to this table it will be seen that when the anterior
surface of only one eye is illuminated Vanessa usually turns
toward the shaded eye when first exposed, but that later it turns
consistently toward the illuminated eye. Consequently, since
it always turns toward the illuminated eye when the posterior
surface is exposed, it is evident that the reactions may depend
to some extent upon localization of the photic stimulus in the
eye.
The results presented in this section show, moreover, that the
tension of the muscles in the legs on either side is not specifically
dependent upon chemical changes in either eye, as demanded
by the ‘continuous action theory,’ for without any change in
the illumination of a given surface of one eye the animal may
turn either to the right or to the left.
GENERAL SUMMARY AND CONCLUSIONS
1. Vanessa antiopa creeps and flies toward a source of light,
that is, it is positive in its reactions to light, never negative.
2. Butterflies of this species, in direct sunlight come to rest
with the head away from the source of light.
3. When placed in a horizontal beam so as to face the light
Vanessa with one eye blackened usually turns toward the func-
tional eye. In some cases it continues to turn in this direction
and consequently performs circus movements both in the beam
and in the shaded region beyond it; usually, however, it proceeds
in a fairly straight course diagonally across the beam until the
edge of the beam is reached, where it usually turns toward the
covered eye and moves directly toward the source of light. Some-
Oe
REACTIONS TO LIGHT IN VANESSA ANTIOPA 417
times the insect does not turn toward the source of light until it
has gone a few centimeters beyond the edge of the beam. The
angle through which the butterflies turn before they proceed
toward the edge of the beam, varies in different individuals and
in the same individual under different conditions. Moreover this
angle bears no observable relation to the luminous intensity. It
was found to be the same in 200 me. as in 2000 me.
4. In non-directive light, or before an open window, these
insects move in circles toward the functional eye, and continue to
do so, showing no apparent improvement. This is probably due
to the absence of changes of illumination on the surface of the
eye. Thus, the performance of circus movements is, in many
cases dependent upon the approximately equal illumination of
large areas of the functional eye in all the positions assumed by
the organism.
5. Cireus movements, however, throw no light on the nature
of the stimulus effective in orientation, for the slightest change in
position of the head may produce changes of intensity on certain
ommatidia in the functional eye.
6. Vanessas with one eye blackened do not move in smaller
circles in strong light than they do in weak light, unless it is
extremely low.. On the contrary, the evidence seems to indicate
that the stronger the light is the larger the circles are. These
results also are not in harmony with those demanded by the
‘continuous action theory.’
7. If, however, the intensity of non-directive light is made very
low, Vanessa with but one functional eye deflects neither to the
right nor to the left, and, if it is made still lower, it moves in
circles toward the blinded eye.
8. These animals modify their behavior as the result of repeated
trials. This modification in reactions is shown in three respects:
(1) decrease in the number of circus movements made, (2)decrease
in the angle of deflection and (3) increase in the promptness with
which they orient on reaching the edge of the beam.
9. If the luminous intensity is suddenly changed when speci-
mens of Vanessa antiopa with one eye blackened have oriented in
a beam of light, and are moving toward the source of light at a
418 WILLIAM L. DOLLEY, JR.
certain angle with the rays, the response varies. Usually, how-
ever, if the luminous intensity is suddenly increased the butter-
flies increase the angle of deflection, and if the intensity is sud-
denly decreased, they decrease the angle of deflection. These
results are probably dependent upon the time-rate of change and
are not due to the difference in the amount of light energy received
by the functional eye under the different conditions.
10. Vanessa antiopa with one eye blackened can re-orient. If,
when the animal is moving toward a source of light, the direction
of the rays is changed so that the light strikes the butterfly on
the side of the blinded eye, the organism changes its direction of
motion by turning directly toward the source of light. If the
source of light is moved to the other side of the animal, the
butterfly again changes its direction of motion and goes toward
the light. Thus, with one eye functional, the animals in orient-
ing may turn either toward the side bearing the functional eye,
or toward the side bearing the blinded eye. ‘These results con-
tradict the assumption of the ‘continuous action theory,’ that
orientation is dependent upon the relative amount of light energy
received by the two retinas.
11. Specimens of Vanessa with one eye blackened move in
circles toward the blinded eye when placed in darkness, while in
light they tend to turn in the opposite direction. This shows
that the covering of the blackened eye produces a stimulus. It
also shows that the circus movements toward the functional eye
in the presence of light are due to a stimulus produced by light,
and are not due to stimuli received by the blinded eye.
12. When suspended above a rotating dise with the head
pointing toward the center of the disc, and with only one eye
illuminated, Vanessa attempts to turn toward the illuminated
eye. Under such conditions there are alternate periods of rest
and activity. The stimulus initiating a period of activity is not
due to change in luminous intensity, and hence it must be due
either to internal factors or to the continuous action of light.
13. If, however, the light is so arranged that only the anterior
surface of the right eye is illuminated, the animal may turn
either to the right or to the left. This indicates that the reac-
REACTIONS TO LIGHT IN VANESSA ANTIOPA 419
tions may depend upon the localization of photic changes within
the eyes, and it seems to show conclusively that the tension of
the muscles of the legs on either side of the body is not specifi-
eally controlled by photo-chemical changes in either eye in
accord with the ‘continuous action theory.’
14. The following facts: (1) that Vanessa antiopa with but one
eye functional can orient, (2) that in a beam of light circus move-
ments become less frequent and the angle of deflection decreases
with experience, (3) that the degree of deflection is no greater in
light of high intensity, than it is in light of low intensity, (4) that
Vanessa can turn under certain conditions toward either side
when only one eye is illuminated, and (5) that these insects can,
in the process of orientation, turn either toward the functional
or the blinded eye, all, indicate that orientation in Vanessa is
not wholly dependent upon the relative intensity of light on the
two eyes. They show moreover that the path in the nervous
system along which the impulses travel is not permanently fixed.
Regarding the question as to the nature of the orienting stimulus
our evidence is, however, not conclusive.
BIBLIOGRAPHY
Barrows, W. M. 1907 The reactions of the pomace fly, Drosophila ampelo-
phila Loew, to odorous substances. Jour. Exp. Zoél., vol. 4, pp. 515-
537.
Boun, G. 1911 La Nouvelle Psychologie Animale. Paris.
BrunpIn, THorBoRG Marie 1913 Light reactions of terrestrial amphipods.
Jour. Animal Behavior, vol. 3, pp. 334-352.
Carpenter, F. W. 1903 Reaction of the pomace fly, Drosophila ampelophila
Loew to light, gravity, and mechanical stimulation. Amer. Nat., vol.
37, pp. 157-171.
1908 Some reactions of Drosophila, with special reference to convul-
sive reflexes. Jour. Comp. Neur. and Psych., vol. 18, pp. 483-491.
Hapuey, Puitre B. 1908 Reaction of blinded lobsters to light. Am. Jour.
Phys., vol. 21, pp. 180-199.
Houtmes, 8. J. 1901 Phototaxis in the amphipoda. Am. Jour. Phys.
pp. 221-234.
1905 The reactions of Ranatra to light. Jour. Comp. Neur. and
Psych., vol. 15, pp. 305-349.
1905 The selection of random movements as a factor in phototaxis.
Ibid., vol. 15, pp. 98-112.
1911 The evolution of animal intelligence. New York, pp. 280.
1912 The tropisms and their relation to more complex modes of
behavior. Bull. Wis. Nat. Hist. Soc., vol. 10 pp. 13-23.
MaVOl wo.
420
WILLIAM L. DOLLEY, JR.
Houmes AND McGraw K.W. 1913 Some experiments on the method of orienta-
tion to light. Jour. Animal behavior, vol. 3, pp. 367-373.
Jennines, H.S. 1906 Behavior of the lower organisms. New York, 366 pp.
Keuioae, V. L. 1907 Some silkworm moth reflexes. Biol. Bull. Vol. 12, pp.
Logs,
UE
152-154.
1888 Die Orientierung der Thiere gegen das Licht. (Thierischer
Heliotropismus). Sh. d. phys. med. Ges., Wurzburg, pp. 1-5.
1889 Der Heliotropismus der Thiere und seine Ubereinstimmung mit
dem Helotropismus der Pflanzen. Wiirzburg. 118 pp.
1900 Comparative physiology of the brain and comparative psychol-
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1905 Studies in general physiology. Chicago. Vol. 1, 423 pp.
1906 The dynamics of living matter. New York, 233 pp.
1907 Concerning the theory of tropisms. Jour. Ex. Zoél., vol. 4, pp.
151-156.
1909 Die Bedeutung der Tropismen fiir die Psychologie. Liepzig, 51
pp.
1912. The mechanistic conception of life. Chicago, pp. 227.
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Neur. and Psych., vol. 17, pp. 99-180.
1910 Reactions to light in marine turbellaria. Carnegie Institute of
Washington. Year Book No. 9, pp. 131-133.
1911 Light and the behavior of organisms. New York, pp. 378.
1914 Orientation in Euglena with some remarks on tropisms. Biol.
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1915 What are tropisms? Arch. f. Entw. Mech. Bd. 41, 8S. 251-263.
1916 The process of orientation in the colonial organism Gonium
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ParkeR,G.H. 1908 The phototropism of the mourning-cloak butterfly. Mark
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RADL,
Ki.
tion of the blowfly larva (Calliphora erythrocephala Meigen). Jour.
Exp. Zoél., vol. 17, pp. 213-280.
1901 Uber d. Phototropismus einiger Arthropoden. Biol. Cent.,
Bd. 21, pp. 75-86.
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Ka
VITA.
William Lee Dolley, Jr., was born near Staunton, Va., April
13, 1887. He entered Randolph-Macon College in 1904 and
was graduated in 1907 with the degree of A.B. In 1908 he
was Instructor in Latin at that Institution, and received the
~ degree of A.M. He attended the Johns Hopkins University
during 1909-1910 and 1911-1914, making Zodlogy his princi-
pal subject of study, Botany his first subordinate and Physi-
ology his second subordinate. In 1908-1909 he was Instructor
in English in Randolph-Macon Academy, Front Royal, Va. In
1910-1911 he was Instructor in Biology in Western Reserve
University. In 1911-1913 he was Student Assistant in Gen-
eral Biology and Embryology in the Johns Hopkins Univer-
sity, and in 1913-1914 he held a graduate scholarship.
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